The invention relates to a complementary folding radio-frequency CMOS orthogonal down-conversion mixer, belonging to the technical field of the integrated circuit design and signal processing. The complementary folding radio-frequency CMOS orthogonal down-conversion mixer adopts the capacitance-coupled folding structure on the basis of the traditional Gilbert frequency mixer, thereby increasing the degree of freedom of the DC bias. The complementary folding radio-frequency CMOS orthogonal down-conversion mixer adopts the improved transconductance structure and improves the effective transconductance through multiplexing the current, thereby being capable of keeping higher gain and linearity under lower power supply voltage. The complementary folding radio-frequency CMOS orthogonal down-conversion mixer is suitable for the wireless receiving module supporting the WLAN 802.11b/g standard and has the advantages of realizing higher performance by consuming less power and obviously improving the sensitivity and the dynamic range of the system.