The invention provides an insulating gas state detection system for GIS (gas insulated switchgear) equipment. Sulfur hexafluoride mixed gas is extracted from the GIS equipment and fed into a sample gas chamber; a sensor for gas feature detection is used for detecting the sulfur hexafluoride mixed gas in the sample gas chamber to obtain a resistance signal corresponding to a gas feature parameter value; after zero drift of the sensor and on-site interference signal influence are eliminated through a bridge-type compensating circuit, a voltage signal corresponding to the resistance value is outputted; a signal analysis and processing module is connected with the bridge-type compensating circuit to obtain the voltage signal for performing analog-digital conversion and signal amplification processing, and is further connected with a temperature sensor and a pressure transmitter to acquire a temperature value and a pressure value of the sample gas chamber, and temperature and/or pressure compensation of the gas feature parameter value measured by the sensor are realized. The system has functions of measuring sulfur hexafluoride gas decomposition product content, purity, humidity and the like, and accuracy of gas detection and interference resistance during GIS equipment fault diagnosis are improved effectively.