Calculation of the axial thermal strain is important for the reliability design of gas insulated transmission lines（GIL）. To realize the quantitative calculation of GIL’s axial thermal strain

we established a finite-element model of coupling fluid field

thermal field

and force field. Taking the gas convection into account

we calculated the heat loss of the GIL conductor and enclosure

which was loaded on the finite element model as the excitation to calculate the axial thermal strain of GIL. On the basis of the experimental platform consisting of 126 kV GIL

we experimentally studied the high-current generator

demodulator strain and strain sensors

and the thermal strain. The results show that the temperature distribution of the conductor and the shell has a layered phenomenon. The temperature stratification of the shell is more obvious than that of the conductor. And the axial symmetry of the GIL temperature and the axial thermal strain are similar. The axial thermal strain of the GIL approximately is positively related with the square of the load current and the ambient temperature. With the increase of the pressure

the temperature of the conductor decreases gradually

but the shell temperature and the axial thermal strain of the GIL increase gradually

the amount of expansion increases by 20% from filling 0.1 MPa SF6 to 0.5 MPa SF6. The validity of the finite element model is verified by the comparison between the experimental data and the simulation results.