An antenna calibration system consists mainly of a signal source, an antenna, a first radio frequency mixer, a first local oscillator, an power detecting device, a personal computer, and a servo amplifier. The signal source emits a signal, and the antenna receives the signal. The signal and the first local oscillator, which emits a signal, are emitted into the first radio frequency mixer. Then the first radio frequency mixer emits a signal into the energy detecting device which calculates the signal power, and transmits the power into the personal computer. The personal computer calculates the powers, and then transmits an angle control signal into the servo amplifier. The servo amplifier amplifies the signal, and then drives the antenna pedestal to turn until the antenna is aimed at the signal source. This can calibrate exactly the antenna's azimuth and elevation offset angle.