Abstract: In order to solve the support difficult problem of the full seam chamber in deep coal mining, according to the physical and mechanics features of the ultra thick seam in Hujiahe Mine, a theoretical analysis, numerical simulation and site observation method were applied to the study on the surrounding rock mechanics featu res and deformation failure mechanism of the full seam chamber in the deep mining and a comprehensive mutual compensative support technology with the bolt/steel m esh/shotcreting/lining, floor over excavation/reversed arch/reinforce bar/steel mesh/beam and floor bolt was provided.The site observation results showed that the max accumulated convergence between the roof and floor in the water sump chamber was 20 mm, the convergence velocity between the roof and floor was 1.22 .0 mm/d, the max accumulated convergence between the two sidewalls was 36 mm, and the convergence velocity between the two sidewalls was 2 mm/d.With the reinforcement of t he roof and two sidewall support strength and the reversed arch floor control, the floor loading capacity and the support structure integrity could be effectively improved and the serious floor heave deformation of the soft floor in the full seam gateway of the deep mine could be effectively controlled