Abstract: Aiming at the problem of coal pillar size in fully mechanized coal caving face, A combination study method of theoretical analysis and numerical simulation is adopted for studying the distribution of plastic zone of the surrounding rock of 4220 pairs of roadway under different coal pillar size. Combined with the actual situation of the scene, the reasonable coal pillar size is 10m. Finally, the reasonable coal pillar size was tested in the field, test results show, in addition to the deformation of roadway excavation roadway along the roadway excavation at the early stage is large, rib sides convergence was controlled within 250mm, convergence between roof and floor was controlled within 100mm, this shows that the size of the 10m coal pillar is conducive to the maintenance of the 4220 pairs of lanes, it can satisfy the requirement of normal transportation of roadway. The results can provide a reference for segment pillar setting in other mining area of Chengzhuang coal mine with similar mining conditions.