Abstract: This paper presents a path planning algorithm for printing fractal models which guarantees the accuracy of the boundary details and maximizes the efficiency of 3 D printing process. We divide the printing region into three layers, namely the contour layer, the transitional layer and the inner layer. According to different layers we use different filling processes. The algorithm is comprised of four main steps：（1） adopt offset path for outer layer to ensure the boundary details, and the thickness of the outer layer is optimized by checking the number of feature points in the offset curves under the given threshold value;（2） determine a fair cubic B-spline curve as the boundary between the translation layer and inner layer, and then optimize the layer thickness of the transitional layer;（3） use a single continuous Fermat spiral to fill in the transitional layer and inner layer, and propose a local optimization algorithm for Fermat spiral;（4） optimize the global path in three regions. We provide several examples to demonstrate the effectiveness and the printing quality of our method. Comparisons are also made with previous approaches which show the superiority of our method. Furthermore, our method works for geometric models that are composed of multiply connected regions with complex boundaries.