Abstract: Based on the result of model experiment of a simply supported steel box girder with prestressed tendons, finite element models of a simply supported steel box girder and a simply supported steel box girder with prestressed tendons were established with ANSYS finite element analysis software. The accuracy of the finite element analysis is verified well by the comparison with the result of the model experiment. This paper analyzes the effects of the magnitude of prestress forces, the section area of the tendons and the steel plate thickness on natural frequencies of the steel box girder with prestressed tendons.