Analyzed the rule of the Water Flowing Fractured (WFF) zone\'s development during the fully mechanized top coal caving. Six influence factors of WFF\'s height were selected, viz. mining thickness, base rock thickness, dip angle, uniaxial compressing strength of roof, mudstone proportion in overlying rock, and structure of overlying rock.The height-forecasting model of WFF was established based on the Artificial Neural Net-work techniques, and was applied in the first fully mechanized top coal caving face under sea in China.