Gas Insulated Switchgear (GIS) is one of the most common structures in high-voltage electrical equipment, with relatively simple working principles and structures. However, it requires high stability during operation. In order to accurately measure the specific positions of the opening and closing of GIS isolating switches, a GIS isolating switch state monitoring system was designed based on attitude sensors, and corresponding research was conducted on the relationship between sensor angular velocity, offset, magnetic data, and the opening and closing states of GIS isolating switches. Based on a multi-sensor fusion algorithm and considering the deviation of the precise position of the knife gate over time reflecting the influence of time on the stability of the device, a model for assessing the opening and closing states and health of GIS isolating switches was established. Experimental results show that the system designed in this paper has the advantages of good stability, high accuracy, and strong reliability, and provides judgment basis for maintenance.