Abstract: In order to reduce the cost of roadside filling and ensure the stability of the retained roadway system, the 150202 fully mechanized mining face of Shenlei Coal Mine is taken as the background, and the roadside filling body is made of coal gangue and fly ash as the base material, through orthogonal experiments, theoretical analysis, numerical simulation, on-site measurement and other research methods, the optimal ratio of filling materials and the laws of yield stress and deformation of roadway surrounding rock with different filling widths are studied. The results show that the optimal ratio of gangue filling body is water cement ratio 1∶1.85, fly ash replacement cement ratio of 20%, fine coarse aggregate ratio of 35∶65, and sodium silicate content of 6%; the larger the width of the roadside filling body next to the gob-side entry retaining, the lower the deformation of the surrounding rock and the vertical stress of the coal wall; by comprehensively comparing the stress and displacement of surrounding rock under different widths, it is concluded that the reasonable width of the roadside filling body next to gob-side entry retaining is 1.2 m.