The invention relates to a phase failure protector of an electric motor, comprising a voltage protection part and a current protection part. A three-phase alternating current power supply is connected with a voltage converter, a rectifier, a voltage indication light-emitting diode, an undervoltage protection voltage-stabilizing diode, an amplifier and an NAND gate phase, wherein the voltage indication light-emitting diode is earthed through an overvoltage protection voltage-stabilizing diode and a sampling resistor and is connected with an NAND gate through a NOR gate; the NAND gate is connected with a coil of a relay J1 and parallel ports of a diode; the three-phase alternating current power supply is connected with a current converter, the rectifier, the amplifier and the NAND gate; the rectifier is also connected with a phase failure memory circuit and a current phase failure indication light-emitting diode; and the NAND gate is connected with a coil of a relay J2 and parallel ports of the diode. The phase failure protector integrates the advantages of current collection type and voltage type phase failure protectors of the electric motors into a whole, is suitable for the phase failure, undervoltage and overvoltage protection of three-phase alternating current motors with different voltage classes and has the advantages of economy, practicability, simple structure, reliable performance and convenient operation.