The invention relates to the field of the electronic measurement instrument, and especially relates to a frequency mixing circuit. The frequency mixing circuit comprises an intermediate frequency signal source for producing an intermediate frequency signal in 21.4MHz; the intermediate frequency signal source is connected with one input end of a first frequency mixer through a first low-pass filter, and the other input end of the first frequency mixer receives the signal in 149.6MHz; after being mixed through the first frequency mixer, the signal in 149.6MHz and the signal in 21.4MHz output thesignal in 171MHz to a radio frequency after passing through a first amplifier filter circuit and a second amplifier filter circuit switch in order; the radio frequency switch receives at least two signals of 171MHz; meanwhile, the output end of the radio frequency switch is connected with a first attenuator, and the first attenuator outputs the signal through the third low-pass filter. The frequency mixing circuit provided by the invention is more stable in work.