Abstract: In view of small coal pillar size of roadway driving along next goaf at full mechanized sublevel caving face directly decides the stability of roadway and coal recovery rate. Fully mechanized sublevel caving face 8800 of Nanyangpo coal mine was set as the research background, the combining research method of theoretical analysis, similar experiments and field observation was used to study reasonable size of small coal pillar next goaf in roadway driving along next goaf. Based on key strata theory, a mechanical model of key rock articulated structure in roof of coal pillar was established, and the bearing stress of the coal pillar was derived mathematically. According to the linear calculation method of coal pillar strength proposed by Bieniawski, the width of small coal pillar in roadway driving along next goaf was determined to be 7m. Similar experiment was applied to simulate surrounding rock stability of 7m small coal pillar in roadway driving along next goaf, and field observation test of the roadway surface displacement was carried out. The both results were satisfactory, which verified the feasibility of setting 7m small coal pillar in roadway driving along next goaf of fully mechanized sublevel caving face 8800. It provides important reference and reference for the size determination of small coal pillar in roadway driving along next goaf of similar mining condition.