Abstract: With the increasing mining strength and scale, it is of great significance for safety production to ensure the stability of roadway roof of marble rock mass in tin mining area, and the calculation and study of limit span increase the stability of roadway. According to the current situation of mine, the ultimate span of roadway is analyzed by combining the slab and beam theory, Mathews graphic method and Q system classification, and the change of the ultimate span under the reduction of tensile strength is studied. The results show that the ultimate span of roadway roof is 4.8 m by using the slab and beam theory, and 5.0 m by Q system classification. The ultimate span of roadway is 4.8 m. According to the Mathews graphic method, the actual hydraulic radius value of 2.184 m is greater than the theoretical hydraulic radius value of 2.000 m, and the vertical opening span of roadway is 9.3 m, which exceeds the limit span. Therefore, it is necessary to take treatment measures for the exposed space of roadway opening. The ultimate span of roadway rock mass is 4.2 m when the tensile strength decays by 10%. When the tensile strength decays by 20%, the limit span is 3.8 m. When the tensile strength decays by 30%, the limit span is 3.7 m. When the limit span is reached or exceeded, the roadway should be supported systematically in time to keep the stope stable and enhance the safety of mine production.