A method for improving the rigidity of the case adopts a combined structure of ring ribs, spiral ribs, and grid rib structures, a reinforced area, and the case. According to the known shell radius R of the reinforcement area, the corresponding design elements are determined according to the formula within the initial width of the reinforcement area, and then through the strength calculation and verification, four design elements are accurately selected to complete the grid reinforcement ribs to improve the rigidity of the casing The reinforced area with a width of W is a cylindrical segment or a conical segment; the annular ribs are equidistantly distributed along the engine axis in the reinforced area with a width of W; the spiral ribs between two adjacent annular ribs form a stable The triangular reinforcement structure; the starting point, end point and intersection point of the spiral reinforcement are all on the ring reinforcement. The invention has the advantages of better improving the ability of the casing to bear various loads and containing rotor blades, improving the structural efficiency of the ribs, significantly increasing the rigidity of the casing, and being beneficial to improving the coaxiality of the whole machine and improving the vibration characteristics.