In order to effectively predict water inflow in filled area of the fully mechanized face with large mining height in initial mining，the theoretical calculation formula was applied to calculate the height of water flowing fractured zone in the fully mechanized face with large mining height. In combination with the field drilling data, No. 4 aquifer was possibly connected to water flowing fractured zone. At the same time, the FLAC3D software was applied to numerically simulate for the filling process of backfill mining face, and the distribution characteristics of water flowing fractured zone due to the overlying strata migration was obtained and analyzed, combining with field test data. The results showed that during the process of filling face advance the water flow fracture zone was arch shape. When the working face advanced to 115 m, the thick filling rate was 60%, and the roof water flowing fractured zone was connected with aquifer. So the thick filling rate would be no less than 70% in the process of industry advice. In combination with the field data, the accuracy of the prediction was confirmed. The paper provides reference for safe production of the subsequent face.