Abstract: LTE (long term evolution) technology is an important direction for urban rail transit train-ground wireless communication development. The demodulation performance of LTE-M ( LTE metro) system under interference of different modulation is analyzed, it adopts high-order QAM (quadrature amplitude modulation) baseband modulation and demodulation technology. By establishing a QAM system model, the performance of 16-QAM signal in the channel noise of AWGN (additive white Gaussian noise) is analyzed, on top of which, the general BER formula of M-QAM system interference under different modulation is deduced. Through studying the transmission performance of 16-QAM, the effect of phase difference on interference performance is analyzed. The simulation results show that the demodulation and transmission performance of the 16-QAM signal is most affected by the QPSK modulated interference signal. Since the 16-QAM and QPSK (quadrature phase shift keying) modulated interference signals have a phase shift, compared to AWGN interference, the 16-QAM demodulation and transmission performance will deteriorate under QPSK modulation interference. The different phase offsets of interfering signal have little effect on the system BER (bit error ratio).