The factors of atmospheric circulations in the prediction model, which is built by the downscaling techniques and the partial least square regression for summer precipitation in eastern China, are studied by using the monthly data of the 74 characteristic quantities of the northern hemispheric circulations, and the precipitation at 160 stations over eastern China. The study is based on the occurrence frequency of the characteristic quantity in the best prediction model. The results show that the factors with higher occurrence frequency are the subtropical high systems in the Northern Hemisphere and the Eastern Hemisphere. Next, the subtropical high systems in East Asia also play very important roles, especially the strength and area index of the subtropical high in the western Pacific.