Abstract: To eliminate the pore defects in ingot by hot forging process, the closure of pores in solid cylinders undergoing hot forging is numerically simulated by thermomechanical coupling finite element method. The results show that the closure of pore relies on the local deformation, and the main influencing factors are the ratio of ingot height to diameter, pore shape and friction. An empirical formula, which can be easily used to calculate the critical reduction for closing the center pore, is obtained by regression on the numerical results. The predictions of the empirical formula are in good agreement with those of finite element solution, which indicates that the formula can represent, to some extent, the effects of the main factors on the pore closure. Some principles for pore closure are summarized according to the numerical results and the formula.