Abstract: Rock mechanical properties of shale gas reservoir are vitally important for exploitation.It’s necessary to conduct laboratory study on failure mechanism,mechanical properties and brittleness evaluation of shale,which can provide technical support for drilling and fracturing design.Based on rock mechanical properties of black shale,in combination with laboratory experiments and log analysis,the analysis of brittle failure characteristics and influential factors are performed.Comprehensive brittleness evaluation method utilizing elastic parameters and mineral compositions are proposed.Brittleness calculating process of single well utilizing logging data is introduced.Study results show that shale generally has a brittle fracture characteristic,and failure modes are related to shale type,coring depth,coring direction and loading conditions.Failure mode under low confining pressure is predominantly splitting failure;overall stress-strain curve has a very short plastic yield section before failure.Double shear and single shear failure modes are dominant under high confining pressure.Brittleness of shale samples has a close relationship to elastic parameter and mineral composition.A case study shows that brittleness affects hydraulic fracturing results,and coincides well with width generation capacity and deliverability.Comprehensive brittleness evaluation is useful for understanding reservoir mechanics and selecting fracture section.