Doppler mismatch exists in bi-phase-coded echo signal of radar altimeter when used for matched filtering.To solve this problem,a ground echo model of radar altimeter is established,and based on a thorough analysis of the power distribution of echo signal and the phase characteristics of echo matrix,an echo Doppler detection and compensation algorithm based on all-phase FFT is presented.In this algorithm,the Doppler frequency and phase compensation factor are obtained through the phase difference value of echo matrix,which is measured by using all-phase FFT.Simulation and experiment results show that the algorithm is effective for phase compensation,and the Doppler detection error is less than 0.3 Hz.