流域变换是数学形态学中用于图象分割的一种经典方法.虽然流域变换曾因运算量大、效率低而使得其研究工作遭到冷遇，但也因此出现了一些新的理论和算法，并随着并行手段的引入，又使其重新成为研究的热点 ;同时就近期许多研究成果而言，形式化模型的多样性，使得流域变换的定义、算法和实现，尚缺乏统一的描述和全面的总结.针对这一情况，首先给出了连续域流域变换的严格数学模型和两种离散情况下典型的形式化定义 ;然后分类总结了近年来，流域变换算法实现的新进展 ;最后提出了有待进一步研究的问题.

Watershed transform is a classical method of image segmentation in mathematical morphology. This method, with a wide perspective, has been applied successively into some fields like remote sensing images processing of satellite and radar, biomedical and computer vision applications. Watershed transform is a relatively time consuming task, and the study of this problem has been disesteemed by researchers for its low efficiency. But also for this reason, there appear some new theories and algorithms; moreover, with the development of parallel tools, watershed transform has an increasing attention internationally. As to the resent literatures on this field, variety of formalizing model makes the definition, algorithm and implementation of watershed lack in uniform description. Pointing to this status this paper starts with a rigorous definition of watershed transform for continuous case, followed by two kinds of representative definitions for digital case. The solution of plateau problem is discussed in detail. Then some new watershed algorithms proposed in recent years are classified and analyzed, including watershed algorithms by immersion and by topographical distance. The need to distinguish between definition, algorithm specification and algorithm implementation is pointed out. Finally we present the problems and challenges of future research, including accuracy of watershed transform, problem of over-segmentation, parallelization of algorithms and so on.