Abstract: Microstructure evolution of low carbon Si-Mn Q&P steel during partitioning had been investiga-ted by means of SEM and X-ray diffraction,and variation of retained austenite content and its effects on the plasticity of Q&P steel had been characterized.The results show that partition temperature above 450℃ and the partition time longer than 200 s cause martensite and retained austenite decomposition,at same time lots of white granular carbide precipitate.The partition temperature and partition time deter-mine the content of residual austenite at room temperature.When partition temperature is about 400℃ and partition time is about 30 s,carbon content of retained austenite is higher during partition process,and the content of residual austenite at room temperature increase.With increasing partition temperature,content of residual austenite increases at first and then decreases,while it gradually decreases with the extension of partition time.Elongation and residual austenite content show similar change trend.