The invention relates to a method for decreasing the occurrence rate of transverse cracks of boiler water walls. The method comprises the following steps, from wall temperature monitoring to hole expanding, that when a boiler and the water walls operate, the temperatures of the water walls on the four sides and water wall pipes are monitored correspondingly; a thermal deviation curve showing temperature distribution of the water wall pipes in the water walls on the four sides is drawn according to measured temperature data, and whether water wall pipes located in an overheat area exist or not is judged; and throttling holes corresponding to the water wall pipes located in the overheat area are expanded, wherein after hole expanding is conducted during one time of operation, wall temperature monitoring and overheat judging are conducted in the next time of operation, and throttling holes corresponding to the water wall pipes located in the overheat area are expanded after the water wall pipes located in the overheat area are judged to still exist. By adoption of the method for decreasing the occurrence rate of the transverse cracks of the boiler water walls, the occurrence area and probability of the transverse cracks of the water walls are substantially decreased, and the safety of the water walls is improved.