To study the influencing factors on the thermal characteristics of Gas-insulated Transmission Lines (GIL) in pipe gallery, considering the inductance effect of the enclosure and the temperature effect of the impedance, including external air domain, a three-dimensional finite element method of coupling fluid field and thermal field was established. With this model, aiming at the characteristics of Sutong GIL integrated corridor project, the effects of five factors, such as air flow rate, current, ambient temperature, the pressure of insulation gas and emissivity, on the thermal characteristics of the GIL were studied. The simulation results show that increasing the air speed at an air flow rate below 10 m/s can effectively reduce the temperature of GIL, but with the air flow rate continues to increase the cooling performance is poor. With the increasing of current, the temperature of GIL will rise sharply, the temperature rise of the conductor is much higher than that of the enclosure, and the temperature difference between the conductor and the enclosure will increase. The temperature of GIL is linearly proportional to ambient temperature, and the temperature difference between enclosure and conductor becomes smaller. When the pressure of insulating gas is within the range of 0.5 MPa, increasing the gas pressure facilitates the heat dissipation of conductor, and the temperature changing of enclosure is less than 0.5 ℃. With the increasing of emissivity of the inner surface of enclosure or the outer surface of conductor, the temperature of conductor will reduce while the temperature of enclosure is constant, and the temperature of conductor is more sensitive to the changes of the emissivity of conductor surface.