The present invention discloses a down-converting mixer which is composed of four NMOS switching tubes and a current-electric voltage converter without operational amplifier, and the mixer has the function of image suppression. A differential radio frequency signal VRFP and VRFN which is amplified by the front low-noise amplifier (LNA) is coupled to the source pole of the switching tube with the capacitances of C1 and C2, the grids of four switching tubes are respectively connected to the orthogonal four-phase clock of the local oscillator signal, the drains are connected with each other and form the image-suppression down-converting mixer. With the structure the invention reserves the high linearity of the traditional passive down-converting mixer and obtains a higher noise capacity, andwell restrains the low-frequency noise especially the flicker noise.