Abstract: Single pass compression tests were processed by Gleeble1500 thermal simulator in order to analyze the effects of different deformation parameters on austenite grain size.According to experimental results,the model of dynamic recrystallization and the material database of Q345 steel were made up and written in the material subprogram of Marc.Thermal-coupled Elastic-plastic finite element method was used to simulate the compress process of sample by finite element software-Marc.Different recrystallization functions were applied to simulate and calculate the grain size respectively.The results show that the austenite grain size calculated by the new dynamic recrystalliation model is in good agreement with the measured.