The invention provides a power saver for a three-phase asynchronous motor and a power saving method. The power saver comprises three collecting circuits which correspond to three coils of the three-phase asynchronous motor in a one-to-one mode, three control circuits and a processor. Each collecting circuit is connected with the corresponding coil in series. The three control circuits correspond to the three coils of the three-phase asynchronous motor in a one-to-one mode. Each control circuit is connected with the corresponding coil in series. The input end of the processor is connected with the output ends of the three collecting circuits. The output end of the processor is connected with the input ends of the three control circuits. The processor collects real-time circuit information in the corresponding coils through the collecting circuits. The processor adjusts the voltage and the current of a loop where the corresponding coils are placed under the state that the rotating speed of the three-phase asynchronous motor is not changed according to the real-time circuit information. The power saver can save the power using amount of the three-phase asynchronous motor.