The invention discloses a vehicle-borne radar in-loop real-time simulation test system and a method thereof. The system comprises a tested radar located on a turntable, a driving operation unit, a display, a real-time controller and an upper computer, wherein the driving operation unit comprises a driving operation mechanism and a driving operation signal sensor; the upper computer comprises a virtual test field and a target test and analysis unit; a driving vehicle model and a target vehicle model are included in the virtual test field; the driving vehicle model is used for virtually loading the tested radar; the real-time controller comprises a spectrum measurement unit, a target simulation unit, a motion controller and a data acquisition card; and the spectrum measurement unit comprises a millimeter wave signal transceiver, a millimeter wave frequency reducer, a millimeter wave signal analyzer, a time delay controller, a millimeter wave signal generator and a millimeter wave frequency rising device. Through radar hardware-in-the-loop real-time simulation, driving operation, target simulation, turntable rotation control and millimeter wave delay control, simulation test on the radar in various road conditions is realized.