The invention provides a test tool for a steel plate spring suspension system and a test method thereof. The test tool mainly comprises an iron floor, a gantry frame, various brackets and four servo hydraulic systems, wherein the iron floor is used for fixing the steel plate spring suspension system; the four servo hydraulic systems are used for applying loads to the steel plate spring suspension system. During testing, the four servo hydraulic systems are used for applying vertical, transverse and longitudinal loads to the steel plate spring suspension system, and two of the servo hydraulic systems are used for applying vertical loads. According to the test tool for the steel plate spring suspension system, a road test signal driving spectrum can be input through a control system, and the four servo hydraulic systems are controlled to apply loads to the steel plate spring suspension system in order to simulate the stress condition of the steel plate spring suspension system in an actual road test process, so that test data have good reference and are used for testing fatigue features of parts to be tested, and a reliable test measure is provided for the development and test verification of parts.