Taking Lancang River Basin as a study object, the spatial distribution, intra-annual distribution and evolution trends of temperature and precipitation between 1958 to 2015 were analyzed by using climate tendency rate, MK-test and Pearson correlation analysis, and the diving factors of runoff evolution were revealed. Results indicate that the spatial and intra-annual distribution of the temperature and precipitation is uneven. The upstream has low temperature and few rainfall, while the downstream is on the contrary. The precipitation and runoff distributed uneven in the year, mainly in the summer and autumn. The runoff peak comes one month later than rainfall peak. From 1958 to 2015, the trend of temperature is rising and the trends of rainfall and runoff are falling. Runoff mutation occurred in 2005 and the annual runoff decreased by 21.5%. Runoff reduction is mainly associated with rising temperature and decreasing rainfall. Temperature is weakly correlated to runoff. Precipitation was well correlated to runoff before 2005 while poorly correlated after 2005, especially in summer and fall.