Controlling the microstructure in the final product is significant to metal hot forming at either macroscale or microscale. The microstructure evolution during the hot forming must be fundamentally understood in order to control the microstructure. Elevated temperature contributes to minimize the size-effects of microforming processes and also enlarge the forming limits by microforming. Recrystallization and grain growth during microextrusion at elevated temperature followed by air-cooling were studied using conventional recrystallization theory models and finite element methods. The results showed the microstructure distribution in the extruded billet can be rationally predicted based on the conventional recrystallization theory models. The simulation of the grain size distribution agreed with the experiment. A larger extrusion ratio, a faster extrusion speed and a refiner initial grain all help to obtain a smaller grain size and a more homogeneous grain distribution in the extruded billet.