A system for describing software requirements and simulation model for flexible manufacturing system(FMS) has been developed and implemented using ISLDM/SEM. ISLDM/SEM, a set of software engineering tools, is a software life-cycle support system(LSS) generator. FMS specification language (FSL) is designed to aid preliminary design phase of the software development process and simulation modeling process for FMS. FSL can support to generate complete and consistent specification by analyzing the specification to detect potential errors in the conceptual and descriptive representation of the target FMS.