Abstract
This paper introduces the software design specification and analysis technique for the safety-critical system based on Programmable Logic Controller (PLC). During software development phases, the design should perform an important role to connect between requirements phase and implementation phase as a process of translating problem requirements into software structures. In this work, the design specification features for nuclear Instrumentation and Control (I&C) software are suggested in a straight forward manner. It consists of four major specifications as follows; Database, Software Architecture, System Behavior, and PLC Hardware Configuration. Additionally, correctness, completeness, consistency, and traceability check techniques are also suggested for the formal design analysis.