The structure of dynamic compaction machine’s chassis is box girder which is welded by steel plate. The strength and stiffness of the chassis directly affect the performance of the machine and the safety of dynamic compaction. According to the mechanical characteristics of a 600t•m dynamic compaction machine, the author analyzed the stress distribution and deformation of the chassis under three kinds of working conditions by finite element method. The results show that the finite element method can effectively reflect the overall state of stress and the characteristics of local stress of the chassis. The structure of chassis has sufficient strength and stiffness. The thickness of some parts of the steel plate can be properly reduced. These results provide basis for the further optimal design of the chassis.