Microstructure evolution of C-Si-Mn-Nb,C-Si-Mn-Cr-Nb and C-Si-Mn-Cr-Mo-Nb tested steels during step-cooling process were studied.Effects of alloying element and process data on microstructure and mechanical properties of high strength Nb bearing DP steel were analyzed,to illustrate the relationship between alloy composition design and process control stability during DP microstructure and property control.It is shown that,700MPa ferrite and martensite DP steel is obtained respectively by three kinds of composition tested steel under different step-cooling process.C-Si-Mn-Nb steel with simple alloying design of low cost is provided with low hardenability,and has strong process sensibility during microstructure evolution.DP microstructure of ferrite and martensite of C-Si-Mn-Nb steel just can be obtained by coiling at low temperature of 250℃.The process control stability of C-Si-Mn-Cr-Nb steel is stronger than that of C-Si-Mn-Nb steel,to obtain DP microstructure by coiling at low temperature.C-Si-Mn-Cr-Mo-Nb steel with complex alloying design of high cost is provided with excellent process control stability.Alloy element Mo can promote stabilizing of metastable austenite to obtain F+M DP microstructure by coiling at medium temperature of 600℃. Microstructure evolution of C-Si-Mn-Nb, C-Si-Mn-Cr-Nb and C-Si-Mn-Cr-Mo-Nb tested steels during a step-cooling process were studied. Effects of alloying element and process data on microstructure and mechanical properties of high strength Nb bearing DP steel were analyzed, to illustrate the relationship between alloy composition design and process control stability during DP microstructure and property control. It is shown that 700 MPa ferrite and martensite DP steel is obtained respectively by three kinds of composition tested steel under different step-cooling process. C-Si-Mn-Nb steel with simple alloying design of low cost is provided with low hardenability, and has strong process sensibility during microstructure evolution. DP microstructure of ferrite and martensite of C- Si-Mn-Nb steel just can be obtained by coiling at low temperature of 250 ° C. The process control stability of C-Si-Mn-Cr-Nb steel is stronger than that of C-Si-Mn-Nb steel. DP microstructure by coiling at low tempe rature.C-Si-Mn-Cr-Mo-Nb steel with complex alloying design of high cost is provided with excellent process control stability. Alloy element Mo can promote stabilizing of metastable austenite to obtain F + M DP microstructure by coiling at medium temperature of 600 ° C.