Variation of stable isotope in precipitation effected by meteorological factors, geographic parameters, and other hydrological factors, is a complex dynamic process, with highly nonlinear and multi time scale characteristics. This paper focuses on identifying variation in the stable isotopes in precipitation under changing environment. Based on the stable isotopic composition in precipitation and meteorologic data at Hong Kong station during 1973-2008, the regression analysis, Mann-Kendall,wavelet analysis and correlation analysis methods are used to find out the variation law of stable isotopic composition in precipitation under different time scales and its influencing factors. The results show that there is significant negative correlation between stable isotopic composition in monthly precipitation, temperature and vapor pressure. It indicates an obvious rainfall amount effect, but the temperature effect does not exist. Under seasonal scale, it displays obvious seasonal change that the stable isotopic compositions of precipitation in rainy season (May to October), are more negative than those in dry season (November to April). Under annual scale, the stable isotopic composition in annual mean precipitation changes greatly, and has a downward trend as a whole, which is contrary to those of rainfall, temperature and vapor pressure. The rates of decline are -0.08/year (D) and -0.01/year (~(18)O) respectively. Therefore, isotopic composition variations in annual mean precipitation reflect the combined impact of long-term climate change. Moreover, deuterium excess of annual mean precipitation is small and has no obvious long-term trend, which indicates that the imbalance of evaporation and condensation in precipitation process is not significant; and the precipitation is mainly controlled by tropical storm. In addition, the results of continuous wavelet transform indicate that there are obvious periodic variations with scales 4 a,7-9 a and 16-22 a for the isotopic composition of annual mean precipitation series, and scale 16-22 a is the first period.