Sequential Numbering System(SNS) is one of the production and inventory management system, which is more effective and practical to minor enterprises than Material Requirement Planning (MRP) system or Just-in-Time(JIT) system. The purpose of the paper is the structured analysis of SNS as the first phase of software development. Data Flow Diagram(DFD), Data Dictionary(DD), and Mini-Specs are used to analyze the system through the second level. The result can be exploited to SNS software design and programming.