Base flow is the main supply source of river runoff in dry season. The reasonable determination of baseflow process and its evolution trend is of great significance in water resources, water environment and water safety management. This paper used HYSEP to perform the base flow separation from 1965 to 2011 for the Luoshan station of Yangtze river,and got the base flow of Luoshan station.It chose M-K (Mann-Kendall) analysis method to identify the trend of interannual and annual average runoff, base flow and base flow index distribution. The results indicate that the base flow index is 0.83 at Luoshan station.During the past 50 years,the runoff and base flow decreased;the yearly average rainfall and BFI value show the falling and rising trend respectively but the trend is not significant;the runoff is uneven in a year and mainly concentrates from April to September. Base flow is increased from January to July and reduced from August to December;BFI decreases from January to April and ascends from October to December.The main reasons that impact the process of base flow at Luoshan station may be the human activities and storage function of upstream of Dongting lake.