The effect of die design on coating concentricity of optical fiber at high drawing speed is investigated. In high speed drawing process,the pressure gradient of coating in die determines the magnitude of centering force and the concentricity of coating layers. The results of calculation prove that the flow of coating in conical shaped die can create pressure gradient of coating in die. The shape and size of die have very important effect on the magnitude of pressure gradient. The increase on taper and length of die will increase the pressure gradient,while the increase on diameter of hole can reduce the pressure gradient. Based on the optimization of die design,the average deviations of concentricity of primary and secondary coating layers of fiber drawing at 1800 m/min can be reduced to 1 μm and 2 μm respectively.