The integral structure of the multi-span plastic greenhouse was taken as the research subject, and influence of film-preload on ultimate bearing capacity of the multi-span plastic greenhouse was studied through physical model test and finite element analysis. By using ANSYS 10.0, firstly, temperature load was performed to numerically simulate preload, the computational models of greenhouse structure on six kinds of film-preloads condition were established by imposing temperature load. Then, dual nonlinear analysis to the computational model of greenhouse structure was given on snow load condition. Therefore, ultimate bearing capacity was confirmed by racing the balance path of the loading-displacement curve. According to analyze loading-displacement curve, influence of the film-preload on ultimate bearing capacity could be researched. It could be concluded that film-preload would not affect the integral structural buckling mode of multi-span plastic greenhouse, but would reduce ultimate bearing capacity of greenhouse structure by 17%~63%. 