The transient voltage stability has a close relationship with dynamic load characteristic. The load characteristic of induction motor is the important reason causing transient voltage stability. There have been studies on using the critical clearing time to assess transient voltage stability of load node, but the relevant research ignores the effect of the change of the electromagnetic torque of induction motor on the critical clearing time in fault. In order to obtain the critical clearing time accurately, the critical clearing time which considers the change of the electromagnetic torque of induction motor in fault is researched, the mathematical model of electromagnetic torque of induction motor is established, and the critical clearing time is obtained. The critical clearing time reflects transient voltage stability of load node. Simulation and comparison of EPRI36 node system are conducted in power system analysis software (PSASP), and the result verifies the effectiveness of this method.