Abstract: With numerical simulation，theoretical analysis and field measurement applied，the characteristics of roof failure and its influence factor and determination of support resistance of face during fully mechanized caving were studied, which the engineering background is 1109 fully mechanized caving face production technology in Xichuan coal mine. Research shows that upper immediate roof of 1109 fully mechanized caving face periodically breaking lead to face weighting, and the main factors that influence upper immediate roof periodically breaking were upper immediate roof thickness and overburden weighting. The main factors that determination working resistance of support were upper immediate roof periodic caving span and support face wideth and additional force acting position and the force of lower immediate roof to upper immediate roof away from the coal wall. And it calculated the reasonable resistance of support of 1109 fully mechanized caving face. Field measurement show that ZF6400/17/32-type hydraulic support working resistance could meet the requirements of roof supporting，and could effectively support roof, and ensure face safety production. Key Words: fully mechanized caving face; upper immediate roof; combination cantilever beam; periodic breaking; working resistance of support