The power-law fluid of polymer melts in a coat-hanger die is modeled three-dimensionally and simulated using finite element method, In order to get an optimum coat-hanger die, design equation devloped perviously based on one-dimensional flow model in manifold and slot is employed, From the calculated flow rate distributions, the optimum process condition for maximum flow rate uniformity can be determind, The optimum conditions were mainly dependent on the manifold angle and power-law index of polymer melt, The effects of disturbances of power-law index, die width, slot thickness, and manifold angle from the optimum values are investigated thoroughly, Results show that any departure of process conditions from optimum value decreases flow rate uniformity, The effect of land length is also analyzed, Manifold angle is a primary factor governing uniformity of residence time distribution, Two-dimensional analysis is also conducted and its results are compared with those of three-dimensional to show that application of two-dimensinal model using lubrication approximation in the region of manifold is subject to critical error.