Wind profiler is a kind of clear air remote sense device. The Doppler radar information obtained under rain conditions is mainly results of moving precipitation particles, which causes great wind field calculation errors. It is of importance to distinguish whether echo signals are contaminated by precipitation. An ensemble analysis algorithm,based on the K Means clustering, is applied to acquire the vertical radial velocity threshold for SNR variation, which is further used to decide whether the radar data is interfered by rain drops.The method is tested with the observational data from August to December 2011 and March to April 2012 of the Nanjing CLC 11 wind profiler. The results show that this method can be used for distinguishing precipitation and clear air data at different heights, as well as decide properly whether echo signals are contaminated.