| Using several winter wheat varieties of different drought-resistance as materials, the roots characteristics and relations to WUE under varies water conditions were studied by hydropo- nics culture, piped and field experiments. The main results were as follows: From genomic polidy 2n→6n in wheat evolution, roots morphological characteristics increased progressively,while Lpr decreased progressively. That is, Lpr was negative correlated with roots morphological characteristics, especially root shoot ratio gravity and root diameter. Although large root diameter decreased Lpr in some way, Lpr varies more remarkably. It illustrated that in evolution there are parts of roots don't absorb water and roots growth redundancy has appeared, thereby plants have stronger resistant ability to the effect of undesirable environment and have increased it's water use efficiency.Different drought-resistant types winter wheat have distinctive Lpr and roots anatomy. The stronger drought-resistance the varieties has, the lower the Lpr, the smaller the vessel diameter and the lager the root diameter and the cortex width. Lpr was positively correlated with the diameter of vessel, indicating that lager diameter was benefit to decrease axis-resistance of water transportation. Lpr was negatively correlated with the root diameter and cortex width; this suggested that the main resistance to water flow did not reside in only one cell layer, because the longer the radial path to the xylem, the lower the Lpr and cortex width had a closer connection with Lpr. Therefore, Lpr could be regulated effectively by adjusting vessel diameter, root diameter and cortex width.Roots characteristics and the relations to WUE were studied through pipe experiments under water stress. It was found that WUE reflected diversities of vary varieties and different treatments accurately. The stronger drought-resistance the varieties has, the higher the WUE and the morphological characteristics parameter. There was a significantly positive correlation between WUE and length, DW and surface area of root in different varieties, and root length had the strongest significance, which made a further evidence on importance of root length to economic yield. Therefore, WUE could be improved by selecting roots characteristics. Using several winter wheat varieties of different drought-resistance as materials, effects of water stress on ground growth and yield were studied. The results showed that water stress decreased gas exchange parameters,growth and yield characters. But speak at all, The stronger drought-resistance the varieties has, the larger photosynthesis speed, grain number, biology yield ,sample fringe number, economic yield and kilo-grain weight. It indicated that effects of water stress on ground growth and yield have close relation to the drought-resistance. Under the condition of hydroponics culture in climatron,the effects of water stress on chlorophyll fluorescence parameters of winter wheat seedlings of three varieties with different drought-resistance have studied．The results showed that under water stress,winter wheat seedlings variable fluorescence (Fv),maximum fluorescence (Fm),the ratio of the variable to maximum fluorescence (Fv/Fm),the ratio of the variable to minimal fluorescence (Fv/Fo) and the photochemical quenching coefficient (qP) decreased,while the minimal fluorescence (Fo) and non-photochemical quenching coefficient (qNP) raised．Analysis indicated that photosystem Ⅱ damaged,and primary light energy conversion of PSⅡ(Fv / Fm),potential activities of PSⅡ(Fv / Fo) decreased；photosynthetic electron transport,photosythetic primary reaction inhibited；heat disseminate which possess photoprotective effect increased．But each parameters varied difference between cultivars under water stress．Except for qNP,other parameters decreased smaller in wheat cultivars with strong ability of drought-resistance,whereas qNP increased greater．This implies that there was a closed relationship between the effects of water stress on...
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