In order to maximize economic and social benefits of crop production in the Heihe middle reach,the water allocations for crops (wheat and maize) in Ganzhou District,Linze County and Gaotai County were optimized. In the optimization,the fuzzy weighted weights method was adopted to transform the multi-objective into a comprehensive benefit weight of crop,and then the weight was applied to the crop water production function. A quadratic programming model of fuzzy credibility-constrained constraint,where the triangular fuzzy number was used,was employed. In addition,the confidence levels of credibility were 0.5,0.6,0.7,0.8,0.9 and 1.0,respectively. Taking the water allocations for crops in year 2011 as an example,the water allocation in different areas are decreased by 3.7 * 10~7 m~3 and the crop yield increases by 1.3 * 10~7 kg,especially,the economic and social benefits are improved by 280 million Yuan and 1 800 people after optimization. Further,in planning year 2020,the water allocations of wheat and maize will be decreased by 4.98%-5.24% and 11.01%-12.07%,respectively,as compared with the status quo of year 2011,thus the water deficit situation can be improved,but still in a state of water shortage. These water allocations under various conditions can provide different scenarios for decision makers.