Abstract: The study was conducted on modification of grouting of broken roof under stratified mining in a steeply dipping coal seam. Considering the geological conditions of stratified mining in the merged coal seams 3 and 1 at the Pansidong Mine, five types of particle size gradation of grouting reinforcement body models were established, a single-axis compression test based on CT in situ scanning was carried out, and the effects of particle-sized paired reinforcement body strength characteristics, crack evolution, acoustic emission signals and micromorphological characteristics were studied. The study showed that: ① With the increase of particle size grading, defects such as pores and cracks in the reinforcement body are affected by the dislocation of the rock and plasma matrix. Large-scale shear belts have been formed, leading to a gradual decrease in the single-axis pressure resistance of the reinforcement body. The 6～8 mm and 8～10 mm particle size grades of reinforcement body are affected by large particle size rocks, and early stress fluctuations are evident. The form of destruction shows a transition from cross-strait destruction, a combination of slash-slash destruction and a slash destruct. ② With the increase of particle size gradation, the hydrated products (AFt and C–H–S) do not form interlaced network structure to fill the pores between the blocks, which leads to the decrease of the overall strength of the reinforcement body. During the loading process, the end of the rock generates concentrated stress, the cut band increases, the sound emission activity is earlier and more frequent, the high-value vibration count increases and the cumulative vibration count grows faster. ③ The CT scan shows that the main fracture of the reinforcement body occurs mainly at the cementation surface between the rock mass and the grout matrix, and rarely extends through the rock. With the increase of particle size gradation, more small cracks in the reinforcement body expand into large opening cracks, and the number of cracks decreases. After the destruction of 0～2 mm, 4～6 mm and 8～10 mm particle sizes of reinforcement body, the proportion of the crack volume V ≤ 0.01 mm³ decreased by 9.5%, 1.6%, 4.0%, and the proportion of cracks V > 10 mm³ increased by 0.1%, 3.5%, 4.9%. The graying value of the crack increases, and the proportion of the crack volume increases to form a more complex crack network. Based on the test results, the drilling and grouting construction and netting scheme of broken roof are proposed, which provide a theoretical basis for the stable control of broken roof under stratified mining in a steeply dipping coal seam.