The development of multifunctional protection device for the low-voltage three-phase motor is introduced. The overall structure and the operating principle are discussed and the schematic diagrams of current/voltage input circuit, switch signal input, switch signal output, and communication interface are given. This paper analyzes the operating principle of start-up out-time protection, locked rotor protection, unbalanced current protection and overheating protection, and also introduces the hardware configuration and the typical application circuit. The protection device combines with protection, measurement, control and communication, which has the features of perfect function, cost-effective and high reliability. It can provide full protection for the various faults of the low-voltage three-phase motor, and improve the utilization and extend the service life of the motor.