Packing phase control during injection molding process plays a crucial role in ensuring the product quality. As one of the hot topics in the field of polymer precise injection molding, quality control of injection molded parts has always been of concern. In this present study, a part weight control method based on the cavity pressure-temperature during the packing phase was proposed. Experimental results illustrated that the proposed method, which used cavity pressure and Pressure-Temperature (P-T) control as filling-to-packing switchover mode and packing method respectively, was an effective approach for the part weight control. Typical crystalline material (polypropylene) and amorphous material (ABS) were chosen to further verify the feasibility of the control method, and experiments had shown to yield consistent conclusions. The experimental results and conclusions presented in this paper will be useful for proper setting of injection molding process.