Flow of non-Newtonian fluid following power-law model in coat-hanger die has been studied through 2-dimensional and 3-dimensional model. Finite element codes for numerical simulation were developed for each model. The mathematical model of coat-hanger die was constructed according to the analytic design equation based on one-dimensional flow rate distributions, pressure distributions, streamlines, and pathlines were calculated for comparison between two models. The validity of the two-dimensional analysis was investigated based on the three-dimensional analysis. The two- dimensional model was found to be inadequate in regions of the manifold and the die side wall. There was a significant difference in the flow rate distribution and the total pressure drop between two models.