The invention discloses a dual-frequency-band vital sign detection radar system based on superheterodyne and low-intermediate-frequency structures. The system comprises a receiving antenna and a transmitting antenna； the receiving antenna is connected with a low-noise amplifier, a first frequency mixer and a band-pass filter in series； the first frequency mixer is connected with a first low-pass filter； the first low-pass filter is connected with a first analog-digital converter； the band-pass filter is connected with a second frequency mixer, a second low-pass filter and a second analog-digital converter in series； the transmitting antenna is connected with a power amplifier； the power amplifier is connected with a power synthesis structure； one path of the input end of the power synthesis structure is connected with a second phase-locked loop chip connected with the input end of the second frequency mixer, and the other path is connected with a power divider； and the input end of thepower divider is connected with a first phase-locked loop chip, one path of the output end is connected to the input end of the power synthesis structure, and the other path is connected to the inputend of the first frequency mixer. According to the system, the problems of direct current bias and image rejection can be solved at the same time, so that the detection effect of vital sign signals with higher precision is achieved.
