As a knowledge-intensive activity, successful complex product design relies on the ability to effectively manage and share engineering knowledge and experience among the whole company. Since complex product design tasks are usually decomposed into work packages, organizing the knowledge in a task-oriented way is conductive to providing the knowledge service to designers. To this end, we propose a task-oriented complex product design knowledge space model with the dimensions of the design phase, design object and discipline area. As the basic unit of knowledge space model, the design task knowledge unit is classified according to product design knowledge service requirements. After that, a knowledge graph-based knowledge representation framework of complex product design is proposed, which includes knowledge graph layer, RDF (Resource Description Framework) layer and the resource layer. The data schema of complex product design knowledge graph is designed and modeled based on ontology. Finally, a case study of gas turbine blade modeling is given to validate the feasibility of the proposed method.