Abstract: We focuses on insulation degradation monitoring of electromagnetic coils which are fundamental energy conversion components and have been widely used in solenoid valves, motors, and transformers, due to that electromagnetic coils have been shown to be failure prone in reality. First, we theoretically prove that there exists correlation between the coil resonant frequency and the insulation degradation by the coil equivalent circuit model and the insulation failure mechanism analysis. Second, we perform thermal accelerating degradation tests on a solenoid valve coil and the result shows that coil resonant frequency decreases during the test, which validates resonant frequency as the on-line health monitoring parameter for the coil. Finally, we propose a framework for constructing a management system for transparency of degradation states of manufacturing equipment/key components under Industry 4.0 aiming at the practical requirements of smart factory.