The intelligent single-phase motor protector is constructed by current transformator, voltage transformator and single-chip microcomputer. Its working principle, circuit composing and software design flow are introduced. The design uses the characteristics of super anti-jamming and precise control for STC12C5A60S2 single-chip microcomputer. Combining DC sampling circuit, the protector can cut off the power supply quickly and alarm when the operating current of voltage exceed the given ranges. It has the advantages of simple configuration, quick reaction, stabilization and reliability, so it can be applied to the voltage fluctuation and unwatched environment.