Abstract: In order to improve the computing efficiency in practice,a fast distance transform algorithm for 3D image is proposed.Firstly,a 3D image is transformed into several slices of 2D images,for each 2D image two marked arrays are defined.Then,the distance transformation of each pixel in the 2D images is calculated according to the marked arrays,using the contour scanning method.Finally,the distance transformation of each pixel in the 3D image is calculated based on the results of the 2D distance transformations.The proposed algorithm is easy to implement and the experimental results show it demonstrates a significant improvement in reducing time and space complexity,comparing with the existing boundary striping and Voronoi-based algorithms,and thus it has stronger practicability.