In order to resolve the problem of requirement reuse during software development process, activity graph in unified modeling language(UML) was extended to be applied to modeling for software requirement capturing and describing. Description language of requirement pattern based on process model was presented by referring to the usual describing mode of pattern. Definition of the language included name of pattern, domain, context, problem, forces, solution, implementation, examples and related patterns. Descriptions of context, solution and related patterns were defined, and guidelines for development and implement of requirement patterns were given. The description language of requirement pattern implements reuse of software requirements and its application can increase efficiency of software development.