The contamination of HV insulator directly affects the safety and stability of the railway power supply system. A detection device of HV insulator’s leakage current was designed based on ARM microprocessor. The device could detect the leakage current of the insulator and the temperature and humidity parameter of the environment at the same time. The noises were filtered through wavelet transform and the insulation conditions were determined by fuzzy neural network. The designed device more accurately detect the HV insulator’s leakage current and judges the contaminant insulation conditions of HV insulators.