Grid computing is innovative information service infrastructure for dynamic and distributed resources sharing and collaboration. Grid workflow is used to handle tasks with control and data dependencies , and plays an important role in grid computing. It is essential to design an appropriate model to satisfy the distributed and heterogeneous workflow systems that must be flexible, reusable, dynamic feature in higher level. As the idea of the designing and composing semantic Web services, a method for designing grid workflow system framework based on ontology is proposed in this paper. Four types of ontology concept are defined: workflow_meta ontology, model_driven method ontology, knowledge representation ontology and date types ontology, and the particular description of their functions, constitutes and relations with each other are given. Based on this framework, the grid workflow systems will have stronger capability to deal with their cooperation and dynamic composition with each other.