High-voltage disconnector is widely used in power system, but its debugging and maintenance has not been paid enough attention, resulting in a high failure rate of disconnector. At present, there is no quantitative detection standard for mechanical faults which account for a large proportion. In this paper, the output power of the motor is chosen as the characteristic parameter to judge the mechanical state of the disconnector, and the horizontal telescopic disconnector is taken as the research object. On the premise of not removing the secondary circuit, the buckle type current sensors and improved voltage sensors are used to measure the current and voltage of the motor. Combined with the internal power transfer relationship of the motor, the output power curves of various states are obtained. Under the simulated jamming state, the average value of output power is smaller; the closing and opening area ratio is less than 1 when the balance spring fails. Accordingly, a detection method of the mechanical state of the disconnector based on the output power is proposed, which realizes the rapid judgment of the mechanical fault types.