Abstract: In order to study the deformation failure characteristics of fractured deep coal rock mass with high in situ stress and its modification strengthening mechanism,firstly,the in situ stress distribution characteristics of coal rock mass with buried depth about 500 m and 1 000 m were tested by means of small borehole hydraulic fracturing method in field.The in situ stress characteristics in different buried depths,coal rock mass rupture strength and its typical fracture features were studied by comparative analysis.The Mohr envelopes formula of fractured coal rock mass with different buried depths were put forward.The deformation characteristics of coal rock mass fractures with different angles and different stress levels in different buried depths were studied through numerical simulation,and the main influence factors for coal rock modification strengthening with deep buried depth were discussed based on the relationship between the strain energy release rate of fracture development and specific absorption rate.The cantilever beam mechanical model was built,and then the relationship between fracture propagation critical load and different fracture angles was analyzed through Griffith fracture failure criterion.With field testing and numerical simulation results,based on the rupture strength statistic analysis of coal rock mass with different buried depths and technology and equipment required,the modification strengthening principles of fractured deep coal rock mass and its relevant modification pressure critical range were put forward.Based on the above mentioned achievements,the underground testing was conducted in the haulage roadway of 111307 working face of Kouzidong coal mine in the Xinji mining area,China,and the fully process modification and strengthening grouting pressure curve was derived.The grouting diffusion in different modification and strengthening phases of fractured coal rock mass were analyzed,the maximal grouting pressure was no less than 30 MPa,and its normal scope was 15 MPa to 20 MPa.All of the results were accord with the criteria that put forward above.The grouting stone features from sizes 2 μm to 20 μm were verified by field sampling and laboratory SEM testing,the elastic modulus effect of interface between coal rock mass and grouting stone was analyzed by means Nano indentation test,the modification strengthen was verified as good from macros to micro size.