A method and a system for three-phase detection of a three-phase electric device are provided. The system includes a testing circuit and a comparison module. The testing circuit generates two reference voltages by using the three phase voltages of the three-phase electric device. The two reference voltages are the first and second phase voltages with reference to the third phase voltage, respectively. Three-phase detection is performed by comparing the two reference voltages for a determined number of times. After testing is completed, the testing circuit is switched off by the comparison module, to save power.