Long-term tests under axial compression were carried out on 16 steel tube-confined concrete-filled steel tube columns and two concrete-filled steel tube columns for 350 d to investigate the long-term deformation performance. The main research parameters were stress ratio of the core concrete (0.5,0.50, and 0.65), total steel ratio of the inner and outer steel tubes (5.8%, 10.5%, and 15.0%), and the steel ratio between the inner and outer steel tubes (0.0,1.25, and 2.23). The working mechanism of the steel tube-confined concrete-filled steel tube columns under long-term axial compression was analyzed, and a theoretical calculation method for long-term deformation of steel tube-confined concrete-filled steel tube columns was established. Results show that the long-term deformation increased with the increase in the stress ratio of the core concrete, and decreased when the total steel ratio and the ratio between the inner and outer steel tubes increased. The comparison between the theoretical and test results shows that the long-term deformation increased with the decrease in relative humidity. When different concrete shrinkage and creep models were used, the influence of relative humidity varied, and the CEB-FIP 2010 model had the best performance. Therefore, the CEB-FIP 2010 model with 100% relative humidity is recommended for the calculation of steel tube-confined concrete-filled steel tube columns under long-term deformation.