Abstract: To increase the frequency and improve the wind resistance properties of cooling towers, stiffening rings and ribs are added on a cooling tower, and the influences of their dimensions, locations and amounts are analyzed. The stiffening rings at an appropriate location will increase the frequency significantly, but the stiffening ribs have no such effect. The contributions of the stiffening rings to the frequency are decided by their participation degree, so the stiffening rings will have more significant effects if they are located where the mode displacement is large or the modes have more circumferential wave numbers. In practical applications, the frequency will be increased notably if there are 3-5 stiffening rings scattered along the shells with a uniform distance.