In order to overcome the unsatisfactory segmenting results such as over-segmentation, under-segmentation and touched region with holes in particle image, an improved segmenting algorithm was presented. Based on the boundary tracing segmenting algorithm, the proposed algorithm controls the segmenting process with the local maximum value point information of the true Euclidean distance to decrease the occurrence of over-segmentation and under-segmentation. And for the touched region with holes, the inner boundary was traced also, while the outer boundary was traced. The experiment result shows that this algorithm has acquired better segmenting effect.