The invention discloses a method for testing the response time constant of a main servomotor of a hydraulic turbine governor, comprising the following steps: setting the adjustment parameters of the governor under the condition that the hydraulic turbine is in a static state; applying an absolute-value gradually increased positive-negative frequency step disturbance signal of the governor under the condition that the governor is in an automatic state, starting or stopping the main servomotor of the governor at a certain constant speed, moving a main distributing valve to a certain position inthe starting or stopping direction from the middle position, and recording the speed of the main servomotor and the displacement of the main distributing valve; and calculating the response time constant Ty of the main servomotor according to the data obtained in the steps. The testing process is simple, and only a series of positive-negative frequency step disturbance tests is carried out. The data used in the test, comprising the main servomotor stroke, the main distributing valve displacement and the adjustor output yPID, can be easily collected.