The Pre-stressed Hardening Grinding (PSHG) is presented combining with the advantages of Pre-stressed Grinding and Grinding Hardening. In order to study the variation mechanism of metallographic structure and the residual stress within hardening layer under PSHG, the paper took 45 steel as the experimental object and carried on the PSHG experiment. The surface hardening layer with little residual stress was obtained from it. The surface hardness, the wear loss and residual stress were measured and its metallographic structure was observed. Combined with experimental result and the simulation of grinding temperature field, the paper studied the mechanism which the pre-stress influences the metallographic structure and the residual stress. The study shows that parent-phase-hardening and strain-inducing-phase-changing due to applying pre-stress have comprehensive effect on the martensitic phase transformation in the grinding process. And its result indicates that the pre-stress restrains the phase transformation with grinding hardening layer firstly and then promotes it. And then pre-stress affects the residual stress mainly through affecting phase transformation in the typical PSHG. It has the same variation as phase transformation with the increasing of pre-stress in the process.