The ecological flow obtained from traditional hydrologic methods that adopt measured runoff series affected by human activities is lower than its actual value. In order to solve this problem, an improved 7Q10 method is proposed based on analysis of long series of rainfall and runoff data, and is used to calculate the minimum ecological flow at representative hydrological stations upstream, midstream, and downstream of the Luanhe River. The results indicate that runoff in the Luan River has been significantly affected by human activities since 1979, and the minimum ecological flow obtained from the improved 7Q10 method is more reasonable than that obtained from the traditional method.