Interpolation plays a very important role in FDM rapid prototyping machine, so it has a direct impact on the velocity and accuracy. Interpolation algorithm in polar coordinates has low cost and the control principle is simple. Given the advantages of the polar coordinate interpolation, detailed analysis and design on FDM rapid prototyping machine interpolation algorithm based on polar coordinate system were analyzed. Moreover, the feasibility of the interpolation algorithm was verified through Delphi programmed visualization software. On the basis of the above, the time intersected method was proposed to optimize the algorithm, so as to ensure the feed speed stability in a cycle, the uniformity of melt drip molding, greatly improving the machining precision.