Abstract: With the rapid growth of air traffic flow and the increasing density of air flying targets, the overlap of secondary surveillance radar (SSR) replies have become a normal phenomenon, the intelligence quality of SSR is seriously affected. The characteristics of overlapping replies are discussed, the main methods of de-overlapping replies are summarized. Based on the decoding conditions of reply pulses, the correct decoding probability of overlapping replies are analyzed, and its general rule is deduced. At the same time, the strategy of improving the decoding accuracy of overlapping replies are further proposed at the system level, and the accurate acquisition of air traffic control target information is realized, which provides a technical guarantee for the intelligence information quality of SSR.