Abstract: With the increasing development of software engineering in every industry and rapid increment of software scale，size measurement is vital for software system at the early stage of software lifecycle.Based on the logical models built during the procedure of requirement analysis，the E-R diagram is used to simplify data flow diagram.Combining with the measurement principle of function point analysis，the simplified data flow diagrams are taken into account for size measurement.Synchronously，the mapping rules and measurement rules are given in detail.A case is introduced to validate these rules.As a result，this improved method is simple and practical.

Key words: size measurement, entity-relationship diagram, data-flow diagram, function point analysis

摘要： 随着软件工程在各个行业的日益深入以及软件规模的日益庞大，在软件生命周期的早期阶段对软件系统进行规模度量显得尤为重要。在需求分析阶段所建立的逻辑模型的基础上，使用E-R图来简化数据流图，并结合功能点分析的度量原理，以简化的数据流图作为度量要素，详细给出了度量简化数据流图的映射规则和度量规则，以实例验证了这些规则的使用方法，简单实用。

关键词: 规模度量, 实体联系（E-R）图, 数据流图, 功能点分析