In this article, a combination of orthogonal design and variance analysis was used to study the systematical effect of vibration pressure, melt temperature, packing cycle, and mold temperature on the tensile property of polypropylene in dynamic packing injection molding (DPIM). The tensile measurement results show that all variables had significant influence on the final tensile property under the present molding condition. Meanwhile, the optimal molding condition to achieve high tensile strength was also obtained in the investigated ranges. Further quantitative statistical analysis revealed the degree of influence of four variables on the tensile property of polypropylene in DPIM. The sequence of the degree of influence from maximum to minimum is as follow: vibration pressure, melt temperature, packing cycle, and mold temperature. These findings provide the experimental and statistical evidences to illustrate that the application of orthogonal design and variance analysis might be an effective approach to systematically study the effect of multiple variables on the final mechanical property. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013