The invention relates to a forming method of a superplastic forming/diffusion connecting four-layer structure of a grid with variable depth-width ratio, and belongs to the technical field of surface wrinkle prevention, and the surface of the four-layer structure formed by virtue of the method is flat and winkle-free. According to the method, in the process of forming a core board into a grid, the grids with different depth-width ratios are different in expanding start time, i.e., the grid with higher depth-width ratio is formed before the grid with lower depth-width ratio, and the grids with approximate depth-width ratios are approximate in expanding start time, so that the contact start time of each grid and a panel at the position of the grid is approximate; meanwhile, in the grid forming process, the air pressure between the panel and the core board is always kept high, so that the part, which is contacted with the panel, of the grid is not subjected to diffusion connection immediately in the expanding process; due to the effects of two aspects, the problem that the panel draws back along with deformation of the core board in a grid continuous expanding process can be prevented, and thus wrinkles are prevented from occurring.