According to runoff data at main hydrological stations in Poyang Lake watershed from 1957 to 2012, we analyze the trend and periodic variation of incoming runoff in dry season by using Mann-Kendall test and wavelet analysis. The variation law is important for us to utilize water resources and protect water ecological environment. Test results show that from 1957 to 2012, runoff of each station shows an increasing trend in dry season, with mean increased margin of 0.199 per year, especially for runoffs in Wanjiabu station, Meigang station and Hushan station under significance level of 0.1; furthermore, runoff at each station in Poyang Lake watershed has obvious periodic features, with main period of 21a, as well as other notable periods such as 5a, 12a, and 28a. This research offers reference for hydraulic construction, ecological environment protection, and rational utilization of water resources in the watershed.