Main frame structure of metal inner cavity is the most important component for bearing workpressure. The designing of main frame structure not only directly effected use and service life of the machine, but also reflected important factor of the main machine whole designing level. Finite element analysis（FEA）was applied to respectively check and calculate the stiffness and strength of the main frame structure under the working status. It is verified that the whole structure of main frame is safe and reliable. The research result provides reference for production and manufacturing of large metal inner cavity squeeze forming machine. 