Abstract: On the basis of analyzing the characteristics of irrigated area drought evaluation and the shortage of evaluation methods, the authors put forward a new model about extension method which is improved and based on Rough sets and unsymmetrical proximity principle. Compared to the original method, it is more logical and reasonable for calculating weights and its time to run is less. In other words, the unsymmetrical proximity instead of maximum subordination principle may solve the problem in the extension method. Through case drought evaluation, the model is proved successful in being applied to drought evaluation of irrigated areas.