A monitoring signal generation circuit of a SPS and method thereof is disclosed. The SPS provides an output current. The monitoring signal generation circuit provides a current monitoring signal related to the output current. The monitoring signal generation circuit includes a simulation current circuit and a control circuit. The simulation current circuit receives a reference voltage and provides a simulation current signal or the reference voltage as the current monitoring signal. The control circuit is coupled to the simulation current circuit and configured to receive the reference signal, the current monitoring signal and an indication signal. During a period when the indication signal indicates that power switches of the SPS are turned off, the control circuit controls the simulation current generation circuit to provide the simulation current signal or the reference voltage as the current monitoring signal according to the current monitoring signal and the reference voltage.