Abstract: This paper highlights idiographic design methods of the ARD3 motor protector, gives hardware and software flow char diagram. According to hardware modules, the article starts description of the hardware modules schematic for detailed analysis, the combination of practical application note here is how to design the hardware, why this design and the advantages and disadvantages of this design. The conditions that motor protector usually works are poor, for the product more stable and reliable performance, needing to use some anti-jamming measures, described in the text of these anti-jamming measures in practical use has proved to be successful. Key words: motor protector;ARD3;protect function;ModBus