The invention relates to a part size calibration method for additive manufacturing, and aims at solving the problems that a part is too long, the form and location precision is insufficient due to expansion with heat and contraction with cold, and the wall thickness does not meet the requirement due to the size of a laser light spot molten pool. The method comprises the following steps that a partcalibration model is created; the calibration model is printed and needed post treatment is carried out; the corresponding size of the printed calibration model is measured and calculated, calibration is carried out according to a calculation result, the calibrated model is printed again and measured, and whether key size satisfies the requirements is verified.