Compared with the overhead transmission line, gas insulated transmission lines (gil) occupies less land area, has higher insulation reliability, and is increasingly widely used in the field of power transmission. under actual working conditions, gil will withstand a variety of voltages, such as ac, dc and impulse voltages. under such conditions, electric charges will accumulate on the surface of the gil tri-post insulator, which will enhance local electric field and affect the surface flashover voltage. based on the measurement method of electrostatic capacitance probe, a surface charge measurement device for gil tri-post insulator was developed in this paper to capture the surface charge accumulation characteristics of tri-post insulator under different voltages insf6. according to the structural characteristics of the tri-post insulator, a set of three-dimensional motion control mechanism is designed to control four probes to scan the surface of insulator in the post zone, the sphere zone and the junction zone of post and sphere with high precision. the calibration experimental results show that the system has high sensitivity and accuracy. for the side probe of post zone, the charge resolution is 0.0290c/(m2·nv) and the spatial resolution is 4.6mm2, for the 1# arc probe of post zone, the charge resolution is 0.0237c/(m2·nv) and the spatial resolution is 5.1mm2, for the 2# arc probe of post zone, the charge resolution is 0.0245c/(m2·n v) and the spatial resolution is 5.0mm2, for the sphere probe, the charge resolution is 0.0165c/(m2·n v) and the spatial resolution is 6.7mm2