The invention relates to an interior filling optimization method oriented at 3D printing. The interior filling optimization method comprises the following steps: inputting the model and the minimum wall thickness of a part to be formed, and determining the forming positions and the slice thickness; acquiring the minimum forming inclination angle of the part to be formed; performing slicing on the solid model; acquiring the corresponding internal contours in sequence from top to bottom according to the input contours of all slice layers in combination with the minimum forming inclination angle; and enabling a filling path to be formed by combining the filling areas of all the slice layers in sequence, and outputting the filling path in the form of a 3D printing path file. The interior filling optimization method oriented at 3D printing has the advantages that the interior filling area of the solid model is optimized on the basis that the formability is ensured, the interior filling volume of a workpiece is reduced, the forming efficiency is improved, and the consumption of the forming material is reduced.