Abstract: In order to improve caving and drawing characteristics of extremely thick coal seam with dirt band, authors studied the mechanical structure of hard and thick dirt band with elastic mechanics theory, based on commingled production engineering of extremely thick coal seam at Luzigou Mine. The“short cantilever' 'structur e formulas of hard and thick dirt band were obtained, when the structure occurred tensile failure and shear localization. They were the main basis of piecewise slotting, when directional hydraulic fracturing between supports was used to crack dirt band. The fracturing piecewise length was determined as 0.8 m, in view of the KZ54 Type slotting drill features. The study results showed that the fracturing pressure curves fluctuated lttlet, which showed that cracks continued to expand forward; after fracturi ng, blocks of dirt band and coal were decreased, and top coal were out smoothly; working resistance of supports increased at the upper end of the No. 3107 face after f racturing. Directional hydraulic fracturing between supports helps to improve top coal caving.