The shape deformation of optical pickup lens in injection molding was investigated in this study. It was realized that residual stresses and warpage deformation in injection molding parts were affected by different process conditions such as melt temperature, mold temperature, packing pressure and time. A two dimensional analysis in injection molding only provides information on the thickness shrinkage for optical lens. In order to simulate the surface contour variations, a three-dimensional warpage analysis was conducted in this study using the finite element method. Moldings under different packing pressures and mold temperatures were numerically investigated to study the effects on the residual stresses and deformation of a molded pickup lens. The packing pressure and mold temperature were found to be the dominant factors that affect the shrinkage of lens in the thickness direction, resulting in surface contour deviation.