Guizhou Caohai wetland plays an important role in climate regulation and biodiversity research. Based on 50a rainfall data of Weining National Reference climate station in Guizhou Province, mathematical linear regression, Man-Kendall test and least square method were used to analyze and forecast the precipitation. The results show that the precipitation of Caohai wetland shows a decreasing trend in recent 50 years, with a decreasing rate of - 12.24mm/10a, and the decreasing trend is not obvious. Seasonally, the precipitation in spring and summer showed an increasing trend, and the trend rates were 1.37mm/10a and 6.15mm/10a respectively. The precipitation decreased in autumn and winter, especially in autumn. 86 mm / 10A. Through the Man-Kendall parameter trend test, the trend mutation test of precipitation in recent 50 years is carried out. The Z value is -0.788, and its absolute value is less than 1.28. It fails to pass the reliability test of 0.9, indicating that the precipitation has a decreasing trend, and the decreasing trend is not obvious, which is consistent with the results of mathematical statistics. Man Kendall nonparametric mutation test showed that the precipitation in recent 50 years had mutation in 1986, 1997 and 2012. During the 30 years from 2019 to 2048, the precipitation of Caohai wetland showed an increasing trend.