Watershed transform is the main tool of mathematical morphology used for image segmentation which can produce one-pixel wide and close edge.This method applied directly to gradient image causes severe over-segmentation.In this paper，the author presents a multi-scale watershed transform based on morphological scale-space by the analysis to the reasons of over-segmentation produced by watershed and the possible under-segmentation due to watershed-plus-marker.The method proposed here could be divided into three steps: (1)The alternate sequential filters(ASF) based on reconstruction are used to reduce some difference inside objects； (2)The closing by reconstruction be applied to gradient image in order to remove some local minima that does not correspond to the maximum and the minimum of the original image； (3)The processed gradient image is segmented using the watershed transform.