The invention provides a method for reinforcing the strength of a sand core used for a car hot stamping mould and obtained by 3D (three-dimensional) printing. A coated sand mould and the sand core required for casting the stamping mould are printed by utilizing 3D printing equipment, and a high-precision casting blank of the hot stamping mould provided with a conformal cooling water channel can be obtained after pouring. But a printing material is coated sand, resin in the coated sand loses efficacy at about 600 DEG C, and the strength of the sand core obtained by 3D printing is reduced at a high temperature, so that the sand core needs to be subjected to strength reinforcement treatment. The invention provides a method for penetrating the sand core by a molybdenum wire or burying the molybdenum wire in the sand core and enabling the molybdenum wire to serve as a core bar, so that the heat resistance time of the sand core at the high temperature can be prolonged and the hot stamping mould in which the cooling water channel is completely unblocked can be obtained.