Abstract: In the enhanced geothermal system (EGS),a low pressure water injection trigged rock fracture shear is a key technique to enhance the fluid conductivity and improve the heat extraction efficiency of geo thermal reservoir.However,the mechanism of hydro shearing under hydro thermo mechanical chemical (HTMC) coupled conditions is extremely complex which has become a key issue for heat extraction and a hot topic for earthquake prevention and control in EGS.Furthermore,lots of new problems arise and many existing theories are no longer fully applicable under high temperature and high pressure (HTHP).This in turn requires that the theoretical innovation,experimental equipment development and engineering technique breakthroughs should be made to promote the progress of geothermal energy development.By reviewing the current research status of hydro shearing mechanism,the authors focused on the topic of hydro shearing mechanism of fractured rock mass under HTMC coupling and clarified some key scientific and technical problems including:① evolutions of the cohesive strength and internal friction under high temperatures;② HTMC coupled effect on hydro shearing criteria;③ applicability and parameter optimization of effective stress theory;④ dynamic failure response of hot dry rock fractures under hydro shearing;⑤ effect of thermal shock on hydro shearing;and ⑥ the relationship between water injecting induced shearing and the possibility of induced earthquake,and potentials about releasing earthquake using hydro shearing technique.By re viewing the mechanism of hydro shearing of the EGS reservoir,the authors would like to summarize and discuss the key scientific and technical problems,thus it may be helpful to have a comprehensive understanding of hydro shearing and promote the application of the technique.