This paper analyzes Chinese patent abstract about alternative energy vehicles by way of knowledge engineering method, and puts forward an Ontology-based knowledge extraction model for Chinese patent abstracts. Main stages in building the model include: to construct a corresponding Ontology, to collect a related word list, to write corresponding rules. These rules are utilized to extract underlying knowledge in patent abstracts. The result aids in the automatic construction of patent knowledge base. This paper is an attempt on how to organize unstructed information and on how to automatically construct a knowledge base, and verifies the feasibility of Ontology-based patent abstracts' knowledge extraction.