The hot forging process consisting of rolling, busting, blocking and finishing for an automotive lower arm connector was analyzed by finite element method (FEM). The process parameters obtained by the analysis such as temperature, strain and strain rate were coupled with physical and mathematical modeling to predict the microstructure evolution during the forging process. The predicted microstructures through the coupled model well agreed with the conventional product and the specimens tested on hot deformation simulator. Various austenite grain sizes were observed in three cross sections because different thermomechanical history was applied, respectively. Especially, under the condition of high value of Z (epsilon exp(Q/RT)) in the blocking process, the austenite grain size of the part was finer than other parts since the size of dynamically recrystallized grain decreased with increasing Z value. It was thought that the austenite grain size in the hot forging was mainly affected by the dynamic recrystallization.