Abstract: Nano-indentation hardness and deformation behavior of the microstructure in the TRIP1000 steel were studied by nano probe experiment.The results show that the microstructure of the steel was mainly composed of ferrite,bainite and residual austenite after heat treatment.The bainite had higher nano hardness at the beginning of yield deformation and twice maximum load bearing as much as the ferrite and austenite.The main reasons on yield deformation destabilization of the TRIP1000 steel were Cottrel latmosphere effect of ferrite and stress relaxation of astable austenite during yield deformation.Stable austenite took place a lot of plastic deformation before stress relaxation and the strain was in strain hardening processing of the macro tensile curves during yield deformation destabilization.