Crop water requirement is very important parameter for making high efficient irrigation schedule, irrigation and drainage planning and scientific allocation of water resources. At present, the main approaches used for simulating crop water requirements include FAO-56 dual crop coefficient method, two source model of conservation of energy, water balance model of root zone and SWAP model. Each approach had its own advantages, disadvantages and applying conditions. No matter which approach is used for simulating crop water requirement, the validity of modeling results should be examined. Otherwise, the simulated crop water requirement could not be used for the engineering projects mentioned above. In the paper, based on irrigation experiments data, the crop water requirements of planted Elymus and Agropyron were simulated by the dual crop coefficient approach. Fitting correlation diagram method, regression analysis and indicating residual estimation errors were also used to examine the validity of simulated results. The first approach was a qualitative test method, and gave statistical correlation trend. Second and third approaches were quantitative test methods, and indicated the goodness of fitting and the ranges of the residual estimation errors. By integrating qualitative approach with the quantitative ones, the consistency between the simulated values and the observed values of crop water requirements was effectively examined, which the simulated results can be applied in the engineering projects.