The influence of thermomechanical parameters on the microstructure and retained austenite characteristics in a hot rolled Al-Si-Mn transformation induced plasticity (TRIP) steel based on dynamic transformation of undercooled austenite was investigated, in an effort to produce a desired microstructure and better control retained content. The results show that strain rate had a minor effect on the microstructure, but the volume fraction of retained austenite decreased with increasing strain rate. Decreasing coiling temperature caused a decrease in volume fraction of retained austenite and decrease in the size of bainitic ferrite platelets. Increasing the isothermal holding time during bainite treatment, the volume fraction of retained austenite first gradually increased then decreased. Moreover, The deformation of undercooled austenite not only can influenc the transformation of bainite, but also can refine the grain size of bainite, increase the chemical and mechanical stabilization of retained austenite.