The invention discloses a microwave photon frequency mixing method, and belongs to the technical field of microwave photonics. The frequency mixing method involves respectively performing photoelectric modulation on radiofrequency signals and local oscillator signals to be mixed, and extracting one first-order sideband signal from modulation signals, obtaining radio frequency first-order sideband signals and local oscillator first-order sideband signals, and performing photoelectric modulation on the two to enable the frequencies of applied optical carrier waves to be the same; and respectively taking the radio frequency first-order sideband signals and the local oscillator first-order sideband signals as the radiofrequency signal input and local oscillator signal input of a 90-DEG light frequency mixer, and performing photoelectric detection on the output signals of the 90-DEG light frequency mixer to obtain frequency mixed signals. The invention also discloses a multifunctional microwave photon frequency mixer. According to the invention, multiple different frequency mixing functions can be simultaneously realized, the stray is small, the linearity is high, and the conversion efficiency is high. Therefore, the method and the frequency mixer are suitable for frequency mixing of large-octave microwave signals.