Study On Stock Price Abnormal Effect Of A-Share Corporations M & A Information Disclosure Under The All-Circulation Orientation

June 17,2008, all Restricted Shares of Sany Heavy Industry were permitted to be tradable, marking the A-share market enter a transitional period of full circulation direction, and the paper called it "All-circulation orientation" period. During this period, the macroscopy environment, structure and sub atomic individual character, operating mechanism of Chinese stock market is presenting a completely new structure, and the market operating efficiency raises rapidly too. In this environment, information disclosure of listed companies in M & A transaction aroused the price level, the existence of insider information, as well as companies in the market's behavior, etc. will be substantively changed. Therefore, previous research findings at home and abroad on the current situation is no longer applicable and it needs to reexamine.This article constitutes of 4 parts and the major content and research conclusions as follows:First, previous research is a systematic combing summary form the theoretical basis for this study. We find that the vast majority of studies concluded that the efficiency of China's stock market reform in the stock before the completion of the Weak and effective, making this article available in the traditional financial theory to study under the auspices of the theoretical premise, but the market is difficult to achieve fully effective.This is because investors expect the nonrational and noncomplete information, however, from the "law of large numbers" point of view, the weak efficient market in the group selection is rational.Secondly, this paper defines the subject of the background for the "full circulation oriented", as well as under the background, the Chinese stock market's changes and the new feature. Using "no basic worth information on stock price response",it definites the concept of stock price exceptional effect under oriented entire circulation before or after the announce of merger information. Some also use the event study on the current stock market efficiency and price effects of mergers and acquisitions events conducted an empirical study:Circulation initial orientation, the efficiency of China's stock market has been significantly improved to achieve a quasi-semi-strong efficient.The third part is based on the empirical study and the research is about information leak before merger announce and insider trade.This text finds after entire circulation,more research centers on information leak and the influence of the role change of insider trade subject. Empirical study finds:the condition of merger information leak has improved a lot and is reaching to the level of pre-semistrong market;the more center of public company'interest the more serious of insider trade,but it doesn't support the conclusion that after entire circulation major stockholder and institution inverstors unite to control stock price and to Insider Trade.The forth part is based on the conclusion of the empirical study and the research is about information leak after merger announce.This article asserts:investors with different investment behavior under the expected, formed after the acquisition of information announcement abnormal stock price effect; there are two aspects of information is expected to play a leading role, which affect the property market is the biggest institutional shareholding. The most significant is the book value, indicating full circulation direction, the behavior of institutional investors have become more mature, serve to improve market efficiency and rational model for investment, the market value of mature markets such as market-based valuation method is a methodology the new valuation standards; transaction attributes are most significant addition to main business and the people to change the actual control the traditional factors, there are specific orientation of the additional period model, investors in this model of "insight", shows all flow-guided investors have significantly increased the quality, indirectly promoting the improvement of market efficiency.In this paper, these studies hope to have the following "contribution":a theory and practice is conducive to the formation of the current correct understanding of China's Stock Market Flow; re-define the current stock market efficiency in China, that the future generations in the standard financial empirical research in the field of theoretical premises; to calm the previous theory of inference based solely on the deduction provide empirical evidence; listed companies'problems under the M & A in full circulation and share price reaction rule to make a modest contribution to investors' strategy choice and regulators'policy-making.