The invention belongs to the technical field of rail traffic vehicle and high-voltage electrical equipment on-line insulation monitoring and especially relates to a multiple-unit train high-voltage equipment insulation state on-line monitoring system, which is used for realizing on-line monitoring of the insulation state of 25 kV high-voltage equipment of a multiple-unit train. Through classification of multiple-unit train high-voltage equipment, characteristic quantity screening, wireless transmission, high-voltage induction power obtaining, expert database and fuzzy function operation, the difficulty that a conventional power system on-line insulation monitoring mode cannot be applied to the multiple-unit train, which is characterized by high-speed movement, single-phase power supply, non-single-point grounding, harsh environment and strict requirements and the like, is solved; and the system comprises a data acquisition unit and an analysis and diagnosis unit. The data acquisition unit is used for extracting characteristic quantity of a monitoring object, and transmitting the data in a wireless manner to the data analysis and diagnosis unit for analysis and diagnosis and signal output. The system is reliable in principle, high in precision, high in accuracy, high in safety and good in reliability, is of great significance to promotion of continuous development of the high-speed rail cause, and has good economic benefits and a broad market prospect.