By study on die-punch gap of hot stamping mold for a door anti-collision beam, it was obtained that, when the gap was designed, not only thermal expansion of steel plate but also that of die and punch should be considered.Through simulation and experiments about influence of the gap to hot stamping quality, the following results were obtained that, too great or too small of the gap would lead to much greater of thinning rate and stress, the reasonable gap of die for door anti-collision beam was 1.1~1.2 times of steel plate thickness.