Magnetism switch is the key equipment in coal mining system，the coal mining magnetism switch intelligent monitor system studied in this paper takes the PIC16F877A micro-controller as its control core, intelligently controlling the motor starting and suspending ,at the same time protecting and monitoring all kinds of troubles. The system has many functions such as protection, control, measuring, display, setting, self-diagnosis and communication and so on, the device also has protective steps of leakage locking, short-circuit, overload, phase-failure, under-voltage, over-voltage and so on, and it also could display operation and fault complexion using liquid crystal display and it also could have the system for inquiring about fault and communication. So the device could largely improve the rate of trouble shooting, manufacture efficiency, and save lots of persons and materials and so on .it also largely improves the electrical automatization level in coal system. In addition, the paper also analyses and studies all kinds of interference signals preventing the system from regular operation. The paper concentrates on the intelligent monitor device’s design thoughts, operation principles ，hardware constitutions and so on, discusses all kinds of protection functions, the cause of interference signals and treatment measures. The key words: PIC16F877A micro-controller；Intelligent monitor system；Protection；Interference
