Abstract: The influence of rainfall on the yield of, winter wheat in North China has been estimated by the application of R. A. Fisher's methodl3 of orthogonal polynomials. Data of winter wheat yield during 1955-57 of 11 localities in North China have bean.. used. The results show: 1) a high correlation between the total rainfall of the growing season and the yield, 2) an increase in the yield caused by an additional rainfall at any time during the growing season 3) the highest effect of additional rainfall on the yield occurs during early wintering and around blooming stages. During. these two stages every. additional milimeter of rainfall may increase 0.4-0.45. catty per mou.