Aimed at the problem that the brake disc spring of wet brake of some rubber tyred vehicles is broken during use,the checking calculation of disc spring was carried out with the method in GB/T 1972.It is found that the service life of disc spring under variable load is less than 105 times,which belongs to limited service life.Under the condition of keeping the brake performance unchanged,the disc spring structure was optimized by increasing the disc spring thickness.After optimization,the design cycle life of disc spring is more than 2×106 times,reaching the infinite life specified in GB/T 1972 standard,and it is consistent with the design cycle life of disc spring specified in JB/T 10917 for industrial brake.