The invention discloses a foundation microwave radiometer system and a calibration method thereof. According to the system, a high-temperature blackbody and a refrigerating absorption load are used astwo-point calibration sources for calibration to replace traditional two-point calibration through an external normal-temperature calibration source and a receiver internal switch noise source, and high-precision calibration can be realized without the need for high-precision temperature control and regular external calibration.