Abstract: The typical character of hysteretic curves of lateral load-displacements (P-) was analyzed based on the experimental results of the planar composite frame, composed of concrete filled steel tubular (CFST) columns and I shape steel beam under sustaining axial load and cyclic lateral load. Parametric study is performed about the factors pertinent to the behavior of load-displacement envelop curves of CFST frames based on nonlinear finite element theory. The results show that the parameters, such as the steel ratio of the CFST column, strength of steel and concrete, the axial load level and slenderness ratio of the CFST column, the ratios of the beam to column linear stiffness and the beam to column strength, etc., have a influence on the behavior of load—displacement envelop curves. The load-displacement hysteretic model of one story CFST composite frame is established based on the systematic parametric analytical results. The envelop curve model and hysteretic relationship model are verified by experimental and accurate theoretic results respectively.