A color filter manufacturing method for a plastic substrate uses an extrusion process to form a plastic substrate with multiple grooves. Then, it uses inkjet printing method to jet photo resists into the groove of the plastic substrate after defining the primary colors of red R., green G., and blue B. The method can overcome the problem happened in the conventional CF photolithography process. This, therefore, can simplify the manufacturing process, and can apply to the large-area plastic substrate of a color filter.