Taking Cilin Mountain Mine No.9 mining face as a engineering background, a theoretical analysis and pressure observation were applied to study the No. 9 thin seam overburden strata movement . The results showed that the first weighting interval of basic roof was 34m and the periodic weighting interval was 13m. The field observation data had confirmed the reasonable of hydraulic support used in the working face . The behavior of ground pressure was are closely related with the key strata range of caving zone, which viewed that the key layer considered as basic roof was confirmed by comparison of the theoretical analysis result and the actual result. The study results could provide the beneficial references to realize the safety and high efficient mining of the remaining  No. 9 coal seam.