The invention relates to a photoelectric frequency response tester and a test method thereof. The photoelectric frequency response tester is composed of a frequency shift heterodyne module, a microwave clamp module, a radio frequency module and a control and data processing module. The frequency shift heterodyne module is composed of a directly modulated laser to be tested, a tunable laser, an optical switch, an electro-optic modulator to be tested, an optical frequency shift unit, an optical local oscillation unit, a reference source and a photoelectric detector to be tested. The microwave clamp module provides a microwave switch and different radio frequency port use scenes. The radio frequency module is composed of a main microwave source and an amplitude phase receiving unit. The optical switch and the microwave switch are controlled, the frequency relation of the sinusoidal microwave signals outputted by the main microwave source and the reference source is set, and the required spectrum sideband is analyzed through cooperation of the amplitude phase receiving unit so that the frequency response characteristic parameters of the directly modulated laser to be tested, the electro-optic modulator to be tested and the photoelectric detector to be tested can be acquired, additional calibration test of the conventional method can be eliminated, the test cost of the photoelectronic device can be reduced, and the test accuracy and the flexibility and the reliability of the device can be enhanced.