The invention provides a PWM signal locking circuit of a servo driver. The PWM signal locking circuit comprises a signal output circuit and a locking circuit, wherein the signal output circuit comprises a signal input port and a signal output port, the signal input port is connected with a master control module, the signal output port is connected with an IGBT module, and a control chip is arranged between the signal input port and the signal output port so as to control the output of a signal; the locking circuit is internally provided with a trigger and a reset circuit, the trigger is connected with the IGBT module, the trigger is used for receiving a trigger signal sent by the IGBT module and transmitting the trigger signal to the master control module and the control chip, and the trigger signal is locked. According to the PWM signal locking circuit, by setting the PWM signal locking circuit, the IGBT module can be turned off under the condition that the servo driver is abnormal and is locked in a turn-off state, unlocking recovery is carried out until a reset signal is transmitted, and the IGBT module is prevented from being started by mistake to cause overvoltage damage underthe condition that the IGBT module has already been turned off.