TACAN video signal based on Intermediate Frequency (IF) digital technique is a discrete Pulse Amplitude Modulation (PAM) signal, which contains plenty of random filling pulses with large duty ratio.Considering that the envelope extraction method through searching the pulse peaks is not effective at low SNR, a novel method of digital envelope detection was proposed.According to the definitive signal format, a matched filter was designed to determine the arrival time of pulse by detecting the maximum correlation peak.The pulse peak was estimated to get the envelop signal by fitting the whole pulse.Secondly, least square algorithm was used to estimate the bearing parameter.In order to reduce and restrain outliers, intolerable errors were eliminated on the basis of confidence through residual analysis.At last, the final result was obtained by smoothing acquired k bearing parameters.Its effectiveness was verified by the experiment results.Under the power SNR of 0 dB, the estimation error is less than 0.5°, which meets the requirement of TACAN system.