Abstract: In order to explore the feasibility for safe mining under pressure of North-China-type deep lower-group coal seam floor，with the first working face of the lower-group coal with high pressure water in Jibei mining area as an engineering background，combining with nine Ordovician limestone boreholes′ and one Ordovician limestone hydrological observation hole′s data，predicting assessment and zoning of the Ordovician limestone water inrush risk at normal block were analyzed with the water inrush coefficient method and integrated water blocking strength method of floor strata.The analysis showed that there are two regions with the Ordovician limestone water inrush values greater than 0.1 MPa/m.But according to the comprehensive water blocking strength calculation of floor strata，the integrated water blocking strength value of each borehole was greater than its corresponding actual pressure value，and then the ratio of actual pressure value to its corresponding integrated water blocking strength is analyzed.The results indicated that if Ordovician limestone water inrush coefficient is larger，the region with big ratio value of the actual water pressure to its corresponding integrated block water intensity just exists in dangerous zone.It is line with the actual situation.This research provides a new evaluation method for the floor water control during the transition to deep exploitation of coal resources under pressure in Jibei mining area or other areas with similar geological conditions.

Key words: Deep lower-group coal, Ordovician limestone water, First working face, Water inrush coefficient, Comprehensive water blocking strength