Based on the 243 daily precipitation samples and meteorological statistics at the four stations at Lanzhou city and its surrounding area (Yongdeng, Gaolan and Yuzhong) from April 2011 to March 2012, the characteristics of stable isotopes in precipitation, as well as the correlation between stable isotopes and meteorological records, were analyzed. The precipitation equation of Lanzhou city and its surrounding area were calculated through the regression analysis, and the water vapor source of the four sites was tracked by the HYSPLIT 4. 9 model, and water vapor transmission regime was established. Results showed that the precipitation equation of deltaD =7.48 delta18O + 8.13 indicated intense evaporation; delta18O value was low in winter but high in summer; The variations of observed d-excess was stable all over the year, but there was variation in different time periods; The spatial distribution showed that the weighted delta18O value decreased from the west to the east; The linear relationships between delta18O and temperature was positive correlation, but the linear relationships between delta18O and precipitation was negative correlation; The seasonal variations of delta18O indicated that westerly water vapor, local moisture and summer monsoon all had influence on this region in a large scale, but the westerly water vapor played a dominant role. However, the impact of monsoon moisture had a seasonal limitation, mainly during the period from June to early August.