On the background of Xulian Transmission lines in the mining subsidence region, the coal mining status under these subsidence areas was analyzed. The support displacement of the transmission towers because of typical bars’ stability failure was set to be the safety criterion. And the ultimate deformation of the tower attained through analysis was considered as the deformation limit of the tower. According to the expected results of the surface deformation in subsidence area, the reliabil-ity of the transmission lines across the subsidence area was assessed. Analysis shows that the surface deformation of the old mined-out area has little impact on the safety of the transmission tower. However, when coal mining is end, it is necessary to adopt composite foundation, that's because the composite foundation's anti-deformation capability is enough to withstand the impact of the surface deformation. As to the large inclination and the surface subsidence, appropriate technical measures are needed. Currently transmission lines and towers in the subsidence areas were found run-ning in good condition without abnormalities.