| In this paper, a case study in Shunyi County in Beijing was conducted to explore water-saving cropping pattern and technical approaches in North China plain because agricultural development in the region confronts severe water shortage which threatens its sustainability. The idea of water-saving structure of cropping pattern and method are proposed to analyze historical trends of agricultural water resource variation over time in North China region. On the bases of field trial complemented by household survey, anatomy of regional cropping system in North China on water utilization variability was conducted, and water use efficiency of arrangement in pairs or groups between different crops was appraised by means of agronomy, economics and ecology as well. Based on prospect analyses and projection of cropping development in the region, optimization strategy of regional water-saving structure of cropping pattern adjustment was put forward. The results of this research are generalized as follows.(1) Basic idea of water-saving structure of cropping pattern was proposed, which aims to make a sustainable and high efficient use of limited regional water resource by means of structural adjustment and optimization, is supported by water-saving techniques of engineering, agriculture and management, and takes regional water balance between supply and demand into a comprehensive consideration to realize a harmony between ecological, economical and social benefits to the utmost extent.(2) According to characteristic analyses of water utilization of cropping structure, the result was showed in the following. Cropping structure in Shunyi of Beijing tends to be simplified in recent two decades. For example, the main body of cropping structure is double cropping of winter wheat followed by summer corn, in which winter wheat sown area occupies whole area of all crops harvested in summer while summer corn sown area accounts for 80% of it. Meanwhile, vegetable sown area was increased obviously in recent years. Water consumption of wheat, corn and vegetable accounts for over 90% of whole water for field crops irrigation even 96.5% at most. Water consuming crops with simple cropping structure results in gradual depletion of regional water resource, as a consequence, regional underground water table descends at the speed of 0.7m per year which implies an increasing austerity of water shortage in the region.(3) General analyses and appraisal of ecological adaptability of crops to water showed that: rice, vegetable and winter wheat are comparatively inadaptable to the region especially winter wheat with only 0.37 coupling fitness of water requirement to rainfall. For main crops in Shunyi, critical stage of their demand for water is not always in rainy season due to local climate. Relatively speaking, cotton, spring corn, forage corn, soybean and clover are well adaptable to the region. However, rainfall does not meet crops' demand for water in their growth and reproductive season. Therefore, moderate irrigation is indispensable in crop production.(4) Water use efficiency of crops and water-saving potential of different combination of crops was studied, whose result show that: moderate irrigation is indispensable, overdone irrigation does not have a great effect on crop yield and its water use efficiency but decreases cropping benefit because of highercost. Compared with double cropping of winter wheat followed by summer corn, optimized cropping pattern of rye followed by premature rice saves 1500 m3.hm-2 -2000m3.hm-2 irrigation and keeps production value unchanged, while cropping pattern of rye followed by cotton saves 2500 m3.hm-2 ~3500m3.hm-2 irrigation and brings a great increase of production value.(5) Development orientation of water-saving cropping pattern in Shunyi of Beijing was analyzed by means of RCSADSS model. The result showed that: regional cropping structure will not be sustainable if present cropping pattern and irrigation level continue. Under the precondition of water consumption below its total avai...
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