In the reverse link of tracking and data relay satellite system (TDRSS), AM-AM conversion in the high-power amplifier for frequency-division multiplexing (FDM) signals causes severe inter-modulation interference to the signals in different channels. The interference results in distortion of the channel signals. The present work uses power series to analyze the influence of AM-AM conversion on the amplifier’s magnitude consistency among the channels, and establish a mathematical model of the influence of magnitude inconsistency on DOA estimation. Theoretical analysis and simulation results show that AM-AM conversion in high-power amplifier does not affect the offset of the estimated angle, but reduces the spectral peak within the spatial angle and increases the 3 dB bandwidth. AM-AM conversion also deteriorates the DOA estimation performance.