Abstract: In this paper, the two precisely crossdated tree-ring chronologies established in Qinghai Province in Northwestern China were used. The weights of monthly climatic factors to the growth of ring width were obtained by calculating the response function. From these months which had significant weights, the best reconstructing period was set by calculating correlation coefficients between tree ring indices and various combination of season climatic factors. Then we use stepwise multiple regression method to reconstruct the historical climate. By analyzing the two local recon strutted precipitation series, we discovered that there were obviously wet periods, drought periods and rainfall periodic variation