Abstract: The changing characteristics and trends of the precipitation of the Northwest Territories, as well as the impact of drought on agriculture was analyzed. Based on these, using the data of spring corn yield, CI index and corresponding to the precipitation, water demand from 1985 to 2007 in Gansu Province, the quantitative evaluation method of the influence of drought on corn yield was discussed in the paper. With the help of this method, DI index as drought assessment indicators was proposed. The relationship between the relative meteorological production rate and cumulate DI index were comprehensively considered, of which was made a positive analysis, so as to obtain a more reliable evaluation result. Therefore, the paper put forward a reference assessment method, in order to make a scientific analysis and a quantitative assessment of the influence of drought on agricultural production.