Based on the precipitation data at 13 stations in Tianjin from 1986 to 2008， the precipitation characteristics and the weather modification influence are analyzed in this article. The results show that： the spatial distribution of precipitation is uneven， the difference is small in westeast direction， but large in northsouth direction. The rainfall presents a descending trend from north to south， and the isolines are dense in north while sparse in south. The rate of decreasing rainfall slows down from north to south. The difference is obvious in different season， the rainy days and precipitation amount are mainly concentrated in summer, the precipitation is less in spring and autumn while is least in winter. The weather modification does not change the correlation coefficient of rainfall in Tianjin， and it also has little influence on the spatial distribution. These are related to the characteristics of weather modification in Tianjin. The weather modification operations have influence on probability distribution of the raintype， but the influence is small. After comparing the probability distribution of different raintype in 1986-2001 and 2002-2008， we can find that the probability of lightrain days is relatively low while the probability of moderaterain days is higher after the weather modification operations， but these differences are not significant.