Abstract: In order to offer a better instruction to the design of the body of a large-size jigging machine and verify the rationality of the design currently, the 30 m² 3-compartment jigging machine is taken as the object to explore the low-pressure air pressure inside the small air chest and the permissible fatigue stress inside the machine body through theoretical calculation. Finite-element analysis is then made based on the calculated result. As indicated by result of analysis, in consideration of the margin of safety, the air pressure in the chest and the permissible fatigue stress of the machine body should be rated at 35 427.6 Pa and 214 Mpa, respectively. In this instance, for a machine body formed up using 8 mm-thick steel plates and reinforced with steel ribs set at an interval of 750 mm, the machine body is subjected to an equivalent stress of 69.7 MPa and a maximum strain of 0.9 mm, indicating that the body can meet the safety and rigidity requirements. For the design of a large-size jigging machine, if its body is subjected to an air pressure without too much fluctuation, and the reinforcing ribs are set at a certain interval, the body can surely attain the strength and rigidity as required. The work made in the paper provides a certain theoretical basis for the design of large-size jigging machine.