Abstract: Using precipitation data of about 26 stations located in the Weihe River Basin during 1951-2012，the paper analyzed the frequency of precipitation and its impacts to the Weihe River basin. Frequency of precipitation in the Weihe River exhibits a marked seasonality，with the heavy rainfall concentrated in the period July-October. Mann-Kendall test are used to examine the abrupt changes of precipitation frequency of different level and average precipitation. The results showed as follows：（1） the spatial distribution for frequency of precipitation gradually increase from north to south，namely，the highest frequency of precipitation in high value areas is 111.39 d·a^-1，the lowest frequency of precipitation in low value areas is 67.77 d·a^-1 .heavy precipitation exhibited increased gradually from northwest to southeast，the highest frequency of precipitation in high value areas is 8.10 a·a^-1，the lowest frequency of precipitation in low value areas is 1.99 d·a^-1. In the past 48 years，high correlation existed between annual precipitation and the frequency of heavy precipitation, the area exhibited positive correlation account for 96.59% of the total watershed area，and the area exhibited negative correlation account for 3.41%. The paper also found that the frequency of heavy precipitation conforms to the power-law distribution in a certain stage. There is a turning point in the middle of the fitting line，when the scale of frequency of heavy precipitation is larger. Power law distribution laws can explain that heavy precipitation is an important factor which triggered floods of Weihe River basin. The research of precipitation frequency，to a certain extent，is helpful for understanding spatio-temporal distribution of extreme disasters scientifically，and for having scientific management and taking preventive measures.

Key words: frequency of precipitation, Mann-Kendall test, Pearson correlation coefficient, Weihe River basin