In order to study the failure modes and seismic behavior of the connections between the rectanglar steel pipe column and circular steel pipe column in imitated ancient building, four specimens in 1: 1.5 scale of the prototype model were designed and manufactured. The destruction tests on the specimens were carried out under constant vertical load and low cyclic reversed load. The loading process and failure patterns were observed. The load-displacement hysteretic loops and skeleton curves were obtained. The influences of slenderness ratio and axial compression ratio on the failure pattern, hysteretic performance, stiffness, bearing capacity, ductility and energy dissipation capacity were analyzed. Test results show that connections damage at the welds near the root of the flange of the rectanglar steel pipe column. The hysteretic loops of the connections are in plump-shape. The connections have insignificant stiffness degradation and high bearing capacity. As the connections fail, the ductility factor of the story drift is between 4. 17 and 4. 97, and the equivalent viscous damping coefficient is about 0. 445 to 0.537, showing excellent energy dissipation capacity and seismic behavior. Based on the experimental research, finite element analysis software ABAQUS was used to simulate the properties of specimens. The axial compression ratio, yield strength of steel, widththickness ratio of square steel tube were taken as analytical parameters. The numerical simulation analysis results indicate that with the increment of the axial compression ratio and the yield strength of steel, the horizontal loadbearing capacity is improved，but the ductility of the member decreases. With the increment of width-thickness ratio of square steel tube, the ductility of the member is improved，but the horizontal load-bearing capacity decreases. [ABSTRACT FROM AUTHOR]