The embodiment of the utility model provides an equivalence time constant measurement system of system of generator, include: generator, disturbance device, exciting arrangement, measuring device, the disturbance device set up in system voltage both ends in the equivalent return circuit of excitation of generator, exciting arrangement set up in excitation voltage both ends in the equivalent return circuit of excitation of generator, measuring device set up in the quick -witted terminal voltage both ends in the equivalent return circuit of excitation of generator. In this embodiment, the disturbance device produces the same electric power system disturbance extremely the generator makes the generator basis exciting arrangement's excitation limit value gets into excitation amplitude limiting state, under the measuring device monitoring excitation amplitude limiting state the quick -witted terminal voltage curve of the generating line side of generator is followed measure generator system equivalence time constant in the machine terminal voltage curve to the equivalence time constant's of system of the unable direct measurement generator of conventional method technical problem has been solved.