Abstract: Requirements analysis is an extreme important step of software development. A pragmatic approach to requirements analysis and its modeling is proposed in the paper, namely, UML Activity Diagram is used to modelbusiness wor kflow, UML Object Diagr am in conceptual layer, UML St ate Diagram and UML Object Interactive Diagram are used to respectively model structural and behavioral Logic, and UML Use Case Diagram is used tomodelfunctional requirements, maps from requir ements to activities in UML Activity Diagram, and maps from requirements to objects in UML Object Diagram. At t he same time, the important process concepts in the requirementanalysis and constructing algor ithm are discussed in detail. T he approach presented in the paper has got successfulapplication in t he requir ement analysis of SST, namely Space Solar Telescope satellite system.

Key words: requirements analysis, OOA, UML, object oriented methodology, software engineering