Vital signs monitoring is essential to good health. Non-contact vital signs monitoring systems based on millimeter-wave radar offer a solution to the inconveniences associated with contact-based monitoring while ensuring precision and enhancing comfort. It holds significant practical value in the field of medical and healthcare monitoring. Beginning with an introduction to the detection principles and medical applications of millimeter-wave radar, this article briefly elaborates on the functional modules, technical parameters, and vital signs that can be monitored by millimeterwave radar systems. Then, it compares commonly used commercial radar chips in literature, with a special emphasis on discussion of the key algorithms in each signal processing stage of millimeter-wave radar systems. Finally, it summarizes the advantages and disadvantages of millimeter wave radar technology in non-contact vital signs monitoring, and presents prospects for its future development.