In order to evaluate the working condition of swivel flange under high temperature and high pressure more accurately, based on the swivel flange in existing pressure level (300~900 lb), the structure and model of the 1 500 lb and 2 500 lb swivel flange were constructed, and the strength and stiffness of the model were checked. Meanwhile, the finite element static mechanical analysis was carried out by using ABAQUS software. The results show that the calculated stress of the swivel flange under each nominal diameter is less than the allowable stress, and the stiffness meets the requirements. The pressure grade and the flange dimension have certain influence on the stress distribution of the swivel flange, and there are two stress concentration areas in the 1 500 lb swivel flange, which are the high neck of the small end of the hub and the contact area between the gaskets and the flange; In addition to the above two stress concentration areas, the 2 500 lb swivel flange also has stress concentration at the edge of the hub's step. The maximum stress always occurs at the high neck of the small end of the hub, and the maximum stress is less than the allowable stress of the material, so the designed high-pound swivel flange meets the usage requirement. The results of the study further enrich the structural design cases of 2 500 lb swivel flange, and provide some reference for the structure design of high-pound swivel flange.