The relation between the grain yield and surface water resource in Tianjin during 1963-1990 is analysed. Taken the influence of development of society and improvement of agrotechnique into consideration,the tendency equations of grain yield increased with times have been calculated, and the relative yields, after deducting the increase tendency, have been calculated too.The analysis shows that in the year with surface water resource more than 35×109m3,the grain yield decreases,because there is a lot of water logged lowland in Tianjin;in the year with surface water resource less than 35×109m3 and the last year surface water resource more than 20×109m3,the grain yield increases.The relations among rice,wheat,maize and surface' water resource are analysed respectively,and their close relationship are also pointed out.