Main transformer bushing is one of the important equipment in power system, its stability directly affects the safe operation of transformer and power grid. Therefore, the multi-parameter real-time monitoring system of the main transformer casing is developed. Through the mature MEMS technology, the chip level integration of multi-parameter measurement is realized, and the multi-parameter measurement of the main transformer casing is realized. technology, the chip level integration of multi-parameter measurement is realized, and the multi-parameter online monitoring device suitable for hydrogen, oil pressure, partial discharge and oil temperature in oil filled casing oil is developed, including four-in-one sensor, on-site alarm and data processing device, adapter and background background monitoring device. The system is small in size and light in weight, which can realize the on-line monitoring of hydrogen in oil, oil pressure, and oil temperature in oil filled casing oil is developed, including four-in-one sensor, on-site alarm and data processing device, adapter and background display software. The system is small in size and light in weight, which can realize the on-line monitoring of hydrogen in oil, oil pressure, oil temperature and partial discharge and fill the domestic gap.