Abstract: For the neglected problem of roof fragile zone due to the study of roadway roof structure in the macro perspective, the limited span discriminant formula of simply supported beam with unit width under the condition of the stability of beam was established. According to the engineering background, the thickness of weak sandy mudstone, the span of roadway, weak interlayer and fault are the important factors affecting the stability of roadway. By using stratum detector to observe the distribution of roof cracks and separation of strata and combining with borehole column diagram, the hidden dangers of roadway are classified and delineated by taking the thickness of sandy mudstone as the main index. The results show that 311102 auxiliary transportation roadway from the cutting hole to 3# connecting lane belongs to the class IV roof hidden danger area. The supporting parameters of 311103 auxiliary transportation roadway were designed specifically to realize the effective control of the fragile area of the roof.