The invention discloses a microwave photonic down-conversion method based on a dual-drive polarization division multiplexing Mach-Zehnder modulator (PDM-MZM), and solves a problem of poor stability and noise performance in the prior art. The method comprises the following steps of inputting an optical carrier signal; generating a radio frequency signal and a local oscillator signal; setting a direct-current bias voltage of a sub-modulator; generating a modulation optical signal; carrying out beam splitting on the modulation optical signal; detecting the modulation optical signal; and restraining noise by an electric subtraction device. According to the method, the noise is restrained through dual-drive one-time modulation of the PDM-MZM and a difference obtained by the electric subtractiondevice, so that the stability and the noise performance are improved.