Abstract:Through three-dimensional similarity experiment,periodic roof caving regularity of shortwall hydro- mechanical mining along strike is obtained. The shapes of initial roof caving and periodic caving are of triangle and parallelogram plate texture. There is a certain angle between caving line and coal layer strike. The mechanical model of periodic roof caving is established and used to determine functional relationship between allowable area of hanging roof and ratio p of its span along dip to that along strike during periodic caving by approximate analytical method. The application of obtained results yielded good technological and economical benefits and has a guiding significance to the production practice of hydro -mechanized mine.