Abstract: In view of problems of big volume, high maintenance cost, lacking specificity and easy to error operation by use of Window operating system in current online monitoring and pre-warning system of mine ventilator, an embedded online monitoring and fault diagnosis system of mine ventilator was designed. Monitored quantities such as vibration, temperature, negative pressure, voltage and current of ventilator and motor are sent to PLC data collection system through corresponding sensors and intelligent instruments, and the PLC data collection system sends data to Ethernet module. The system can get the corresponding data through protocol analysis, display the data on embedded device and make real-time diagnosis and fault alarming. Vibration sensor, temperature patrol instrument and intelligent electric meter with RS485 communication interface send collected data to embedded bus module through ModBus protocol to realize monitoring and diagnosis functions. Test result shows that the system meets each technical index of online monitoring of mine ventilator and realizes miniaturization and diversification of monitoring device.