To study the eccentric mechanical properties of concrete filled steel tube reinforced concrete column (CFSTRC) under fire, a finite element model is developed. The failure mode, deformation, internal force, strain and stress, interaction between steel and concrete under fire are analyzed, and the results with different parameters are discussed. The results show that under fire, the CFSTRC column shows good plasticity with overall instability failure mode, and the eccentric mechanical response of the column can be roughly divided into three stages. There is a phenomenon of internal force redistribution in each part of the column. With the tensile area of the column section gradually expanding, the interaction force between steel tube and concrete also increases gradually under fire. The section size and slenderness ratio of column have great influence on the bearing capacity of square steel tube-reinforced concrete column under fire.