Based on the elastic thin plate theory, the main law of the ore roof failure was analyzed and the formula of the ore roof thickness was deduced. The results show that the tensile stress in the roof center accounts for the roof failure. According to the limit failure conditions of the point, the formula of the ore roof thickness was derived. Taking No.10 stope of a bauxite mine as an engineering case, the optimal thickness of the ore roof was 0.36 m. The safety factor was taken as 1.3, therefore the design thickness was 0.5 m. In the whole industrial test process, the dynamic alarm devices did not start the alarm and the ore roof was not damaged. Compared with other stopes under similar conditions, its thickness was reduced by 0.1-0.3 m. The recovery rate of the ore roof was increased by 16.7%-37.5%.