Disclosed is a millimeter wave imaging system. The system comprises an emission branch module used for generating millimeter wave radiation signals; an emission antenna array connected with the emission bench module for converting the millimeter wave radiation signals into circular polarized waves for radiation on detected personnel, wherein the circular polarized waves are levorotation circular polarized wave or dextrorotation circular polarization; a receiving antenna array arranged at the same side as the emission antenna array for receiving reflected echo signals, wherein the polarization direction of the receiving antenna array is consistent with the polarization direction of the emission antenna array; a receiving branch module connected with the receiving antenna array for demodulating the echo signals; and an image processing module connected with the receiving branch module for performing imaging processing on the demodulated echo signals and outputting imaged images. The millimeter wave imaging system can protect privacy of the detected personnel and improve the recognition rate of dangerous articles. The invention further relates to a security check system.