The low silicon transformation induced plasticity（TRIP）steel with phosphorus addition at every stage of fast annealing process has been studied by heat treatment experiment at lab. The effects of annealing temperatures on microstructure constitute at every stage are mainly studied. The addition of low price element phosphorus can reduce silicon content， improve surface quality，solve galvanizing problem and reduce costs. Results show that the ferrite content decrease，and the mixture of bainite and martensite content increase at final microstructure. By X-ray diffraction（XRD）analysis，the retained austenite content increases from 12.7 % at 750 ℃ annealing to 14.9 % at 790 ℃.