This study mainly analyzed the effect of hydraulic project on baseflow by the Lyne-Holick filter method, based on the runoff data that was monitored in three hydrological stations, Xiaheyan, Qingtongxia, and Shizuishan, from 1951 to 2000. Results show that baseflows of three hydrological stations were generally similar before the construction of Qingtongxia hydraulic project, all about(184-214)×10⁸m³. Moreover, baseflow data was decreased to(111-187)×10⁸m³ since construction of the project, which indicated that the decrease ratio was nearly 24%. Results by the Mann-Kendall method also shows that, the decrease of baseflow reached its maximum value at the Qingtongxia hydrological station, and the point of abrupt change was observed between 1962 and 1964, which was coincident with the construction of Qingtongxia project. The baseflow index(BFI)of Qingtongxia hydraulic station showed an obvious downtrend in wet years with about 13% and the decrease ratio of BFI was approximately 20% in ordinary years, which provide a valid evidence that the hydraulic projects have strong influence on baseflow.