The finite element program,which has been verified by the full-scale collapse test of steel portal frame structure under fire, is used for simulation in this paper. Then two-dimensional and three-dimensional finite element models are established, and the parameter analysis is carried out. The effects of the heating condition of steel member, foot stiff, span-depth ratio, fire protection, section temperature gradient, load ratio, wind load and secondary components on the collapse mode of steel portal frame structure under fire are mainly studied. Four typical collapse modes are summarized. The results show that the finite element model(FEM) can accurately predict the collapse behavior of steel portal frame structure under fire. The heating condition of steel member, the foot stiff, the load ratio and the secondary component have the most significant influence on the collapse mode, while the wind load, the fire protection, the section temperature gradient and the span-depth ratio have little effect on the collapse mode. In addition, the collapse law of steel portal frame structure under non-uniform fire is summarized systematically.