Chen, J.-R. Chen, M.L. Lai, W.Y. Tsai, Z.-D. Yang, Y.C. JACoW Publishing Geneva, Switzerland The thermo-mechanical stability is crucial to the performance of an advanced light source. The effects of the temperature fluctuations, such as outdoor temperature, air temperature in the tunnel, surface temperature of the major components and the ground temperature in the accelerator building, to the position of the mechanical structure of the 3 GeV Taiwan Photon Source (TPS) were depicted. The correlations and routes of the thermo-mechanical effects were studied.