Theoretical derivation and finite element method were developed in this paper to study the fire resistance performance of mobile house. First, based on the equivalent principle of the critical temperature,the structural deformation curve was simplified as elastic and vertical segments instead of the original elastic-plastic model. Then, deformation formula of the elastic segment was obtained by theoretical derivation, and the method of determining the dividing point was also provided. To this end, the critical temperature formula of frame under fire was obtained. Finally, the fire resistant performance of the entirety house structure and the single frame were analyzed and compared through finite element method. It shows that, the fire resistance performance of the entirety house structure is similar to single frame structure, the number of frame have little effect on the fire resistant performance of entirety house, and the most unfavorable fire location is the middle room.