Abstract:Liangjia coal mine in Huangxian coal field of Shandong Province lies in Longkou Bay. its hydrogeological condition is different from land. Through analysis on drilling data in this sea area, loose layers, coal seam and water resisting layers in roof and floor have been divided. Combining with the servo test results of water filling factors, guiding height of water flowing fractured zone and waterproof coal pillar height have been measured. Thus reasonably waterproof coal pillars have been remained. It will provide important basis for the safety of coal mining.