In order to detect signal of Automatic Dependent Surveillance-Broadcast(ADS-B) precisely, an improved detection algorithm is developed in this paper. And a special match filter for ADS-B is proposed, which benefits from the phase coherence of the pulse train from the first ADS-B preamble pulse to the third format bit. State machine is developed to ensure decode signal in correlate peak. The simulation results show that it is able to increase detection probability by this method under low ratio of signal to noise. The sensitivity of receiver using this method is -95 dBm(the packet error rate is 5%).