The study analyzed the isotopic compositions of rainwater in Chengdu from 1986 to 1998. They found that rain in summer is lighter than in winter, reflecting the monsoon climate. The balance of precipitation in Chengdu is different from global and China norms, indicating an unbalanced condition. The amount of excess deuterium in rainwater was low, suggesting a faint unbalance in evaporation and agglomeration, typical of an oceanic climate. The oxygen isotope composition of rainwater is positively correlated with rainfall, temperature, and water pressure, with rainfall being the most influential factor.