Most transmission parts of the horizontal telescopic type disconnector are directly exposed, resulting in frequent mechanical failures. Its mechanical state is mainly judged by manual operation experience, so it is not easy to achieve rapid and accurate evaluation. In this paper, by establishing the virtual prototype model of the horizontal telescopic type disconnector and building the corresponding test platform, the changing trend of torque in the movement process of the disconnector is analyzed. Compared with the torque-angle curves of the normal state and different mechanical defects’ states, the closing and opening process’s torque increases obviously under the jamming defect. The opening process is torque increases while the closing process’s torque decreases under the spring fatigue defect. The ending torque value of the closing process increases, or there is no typical wave peak in the meshing stage under improper travel defect. There are multiple wave peaks in the meshing stage under the three-phase position asynchrony. With this, the mechanical state diagnosis method of GW23 disconnector based on the torque-angle curve is summarized, and the installation and debugging of the same type of disconnectors in a substation are taken as examples to prove that the rapid and accurate diagnosis of its mechanical state can be realized by using this method in engineering application.