中文摘要：

单位线的建立及其发展，并得以成功应用，是水文科学的重要成就之一。寻觅、回顾了单位线的起源，论述了单位线在处理复杂、特殊的流域汇流现象时的创新性，以及半个世纪以来水文学家为揭示单位线实质采用系统论、物理学、概率论等途径所作的努力及取得的成果。提出了分析和使用单位线所不可忽视的前提条件。由于建立在“网格水滴”概念上的流域汇流计算方法，既能保持单位线法和等流时线法的优点，又能克服这两个方法的缺点，因此有可能在数字高程模型（DEM）支撑下成为新一代的流域汇流计算方法。

英文摘要：

The establishment and development of unit hydrograph as well as its successful application have been one of important achievements in hydrology. The origin of the unit hydrograph is sought and reviewed. The innovation of the unit hydrograph in dealing with complicated and specific concentration flows in watersheds is discussed. The achievements and efforts to reveal the substance of the unit hydrograph by hydrologists over half a century by means of the system theory, physics and probability theory are investigated. The essential preconditions for analyzing and applying the unit hydrograph are put forward. The method for calculating the concentration flows of watersheds based on the concept of ＂grid drop＂ can maintain the advantages of the unit hydrograph method and the isochrone method and overcome their shortcomings. Accordingly, the ＂grid drop＂ will probably be a new generation of the method for calculating concentration flows of watersheds under the support of DEM.