In order to realize multi-channel microwave photonic down-conversion and improve the performance of frequency conversion link. In this paper, a single integrated modulator is used to realize the microwave photonic down-conversion scheme, the scheme uses the polarization multiplexing feature to realize the dual-channel down-conversion function. The simulation and experiment results show that when the sub-modulator is set to work at the minimum transmission point, the carrier-suppressed double-sideband modulation is realized, and the optical carrier-suppression ratio reaches 29 dB. Two channels independently down convert the radio frequency signal to intermediate frequency signals respectively, the spurious rejection ratio reaches about 30 dB, and the spurious free dynamic range(SFDR) of two channels reaches 110.4 dB·Hz2/3 and 113.4 dB·Hz2/3 respectively.