In order to study the insulation performance of environment-friendly gas , this paper studied the discharge characteristics of a linear metal particle on the insulator surface in the mixtures of C4F7N/CO2. The experiment results were analyzed by simulation and theory. The research show that the flashover voltage increases first and then decreases with the increase of the distance between the metal particle and the ground electrode, in the mixture of C4F7N/CO2 gas at 0.1 MPa. By analyzing the above reasons, the space charge generated by corona discharge at the end of linear metal particle weakens the distortion of space electric field. At the same time, the CF3CN molecule produced by the decomposition of C4F7N/CO2 mixture gas is a kind of material with high electrical strength, which can also increase the flashover voltage. The influence of insulator inclination on the flashover voltage of C4F7N/CO2 mixture gas is greater than that of SF6 gas. When the inclination angle of insulator is 90 degrees, the flashover voltage of C4F7N/CO2 gas mixture is 0.96 times of SF6 gas, the electric strength of the two gases is the same. However, the sensitivity of C4F7N/CO2 gas mixture to inhomogeneous electric field is higher than SF6 gas. When the inhomogeneity coefficient of electric field changes from 1 to 1.84, the flashover voltage of C4F7N/CO2 gas mixture decreases by about 26%.