The invention discloses a method for testing a reactive compensation device without dismounting leads. According to the method, under the condition that the leads of various components of the reactive compensation device are not dismounted, the full current of a lightning arrester is measured so as to detect the internal performance of the lightning arrester; the full current or full voltage of the reactive compensation device and the voltage values and current values of the various components like an electric reactor, a capacitor and a discharge coil are tested respectively by switching off the alternating-current operating voltage of the reactive compensation device and adding an alternating-current testing voltage to the two ends of the reactive compensation device. In this way, on the one hand, the quality of the various components can be judged by comparing measured parameters with rated performance parameters of the various components, and a fault phase can be determined according to the deviation of measured results of the full current or full voltage; on the other hand, the component of which measured values have a large deviation can be found by comparing the various components, in the A phase, the B phase and the C phase, of the reactive compensation device through the 'three-comparison' method, and accordingly the fault phase and the fault component of the reactive compensation device can be determined.