Abstract: In order to verify the impact level of climatic factors on summer maize yield in the North China Plain (NCP), some ecological items, including development stage and dry matter accumulation processes, were measured with the field experiments on summer maize at the Yucheng Comprehensive Experimental Station, Chinese Academy of Sciences, located in the North China Plain. Based on the measurements, the crop growth model WOFOST was improved and calibrated. Then the model was used to simulate the potential and rainfed yield from 1961 to 2006 at 42 different stations distributed in the NCP. Results showed that: validation of the model indicated that the model was suitable for simulation of the summer maize growth in this region. Potential yield regionally increased from southwest to northeast ranging from 7360 kg/hm2 to 11370 kg/hm2, with an averaged yield of 9384 kg/hm2. Variance of the first mode contributed to more than 1/3 of the total variance value, and the accumulated variance contributions of the first three modes was as high as 62.5%. Value of the first mode was positive in the whole area, indicating a good uniformity regionally. Rainfed yield ranged from 6160 kg/hm2 to 10420 kg/hm2, with an averaged yield of 7906 kg/hm2, also regionally increasing from southwest to northeast. Accounting for as high as about 1/3 of total variance contributions, the first two EOF modes are obviously greater than those of the rest. By combining crop model simulation with EOF method, for the first time, this research revealed the impact degree of different climatic factors on summer maize yield in different regions of the NCP, based on which theoretical support and practical guide can be given out for the regional agricultural layouts.