Abstract: This paper analyzed the mechanics of a nuclear safety class Ⅱ pneumatic ball valve designed by a valve manufacturer,with ANSYS finite element program.The loads considered in the analysis included gravity,internal pressure,nozzle limit load and earthquake.After the analysis,the paper evaluated the valve according to the standard of ASM and technical specifications of AP1000 nuclear class valve.The calculations showed the design of the pneumatic ball valve can meet the requirement of ASME regulations and related technical specifications.