Through providing the design points of punch and die, the simulation analysis on sheet forming was conducted by software Deform-3D, and the forming of square convex hull with dense row with five rows and four rows (alignment in vertical and horizontal directions), side length b=10 mm and height h≤3.5 mm was tried to simulate on the plastic sheet with 100 mm×130 mm×1 mm. Then, the simulation research was carried out from two aspects of meshing roll bulging device and size parameters of convex hull. Firstly, the necessity of press frame was demonstrated, and then the numerical simulation experiments were carried out in sequence by setting the feeding speed v of press frame, the height h of convex hull and the distance s of convex hull. The results show that the workpiece have problems of flat arching and fracture of convex hull fillet edge. Then, h has the greatest influence on the quality of workpiece. When h is less than a certain value, the workpiece does not appear flat arching and fracture, and the forming quality is good. In addition, changing v is also helpful to improve the fracture problem of workpiece, but it still has flat arching and the minimum arch height is 0.292 mm. Finally, the influence of s on the forming quality of workpiece is the smallest, and there is no significant change.