When gob side entry retaining is carried out in backfill mining, the roof will show different subsidence morphology due to the difference of compactness and supporting force of the backfill body at different positions. This paper analyzed the immediate roof subsidence structure under two extreme conditions, constructed the roof segmented subsidence structure and the mechanical model of roadside backfill body, and used FLAC3D software to investigate the roof migration and the force law of the roadside backfill body under the conditions of different goaf backfilled rates, different width and strength of roadside backfill body. Finally, the backfill practice of a mine in Shandong Province of China is taken as an example for analysis. The results show that the segmented subsidence structure of the immediate roof is related to the mechanical properties of the roadside backfill body and the goaf backfill body. When the backfilled rate of goaf decreases from 95% to 70%, the width of roadside backfill body decreases from 5 m to 1 m, and the elastic modulus decreases from 10 GPa to 0.5 GPa, the greater difference in the subsidence and inclination of the immediate roof on both sides of the roadside backfill body is, the more obvious the segmented subsidence structure characteristics of the immediate roof are, and the greater force on the roadside backfill body will be, the more unfavorable it is to maintain the stability of the roadway surrounding rock and the roadway backfill body. Therefore, when gob side entry retaining is carried out in backfill mining, the surrounding rock structure and the force on roadside backfill body should be considered comprehensively.