Powder forging is an important method for behaviors in a closed die, including the net shape. In order to study the deformation characteristics, the closed die block forging of Ti-Al powder preforms was simulated by commercial plastic forming software DEFORM-3D, using a change of temperature, stress and strain at different regions of the billet. Based on distributions of the stress and strain, the occurrence of defects was analyzed. It indicates that some defects may occur near the edge of preform during the plastic deformation process. At last, the predicted results were evaluated by experiments.