The invention discloses a production method of a three-color co-extrusion plastic profile. The production method comprises the following steps: (1) choosing a PVC basic material and two different ASA colloidal particles; (2) adding the selected PVC basic material and two ASA colloidal particles into a main extruder and two auxiliary extruders, and then extruding the three materials; (3) adding the three extruded materials into a co-extrusion mould to carry out three-color co-extrusion and moulding, wherein the co-extrusion mould is composed of a front extrusion block, a middle extrusion block, and a rear extrusion block, the front extrusion block and the rear extrusion block are both provided with a liquid-storing tank, and the middle extrusion block is provided with a liquid-flowing cavity. The provided production method can guarantee that each part of a mould is uniformly pressed during the co-extrusion process, and thus the thickness of the co-extrusion layer is uniform. The produced colorful plastic profile has the advantages of good linearity, saturated color and luster, diverse colors, UV resistant property, and aging resistant property, is capable of beautifying the environment, and is environment-friendly.