Abstract: This article analyzed the failure and wear forms of coal mining machine gears, and designed an online oil monitoring device based on ferrography technology; based on the current situation of fault diagnosis in coal mine electromechanical equipment, the monitoring and analysis of viscosity and moisture, as well as the monitoring and analysis of wear debris, are used to detect metal elements in coal mine electromechanical equipment, to quickly and accurately detect internal faults of the equipment; the corresponding ferrographic monitoring schemes and diagnostic methods were proposed for common gear faults in coal mine electromechanical equipment.