The problems of the existed acquisition method and representation method for patent technical solution were discussed. A new knowledge acquisition method for mechanical patent’s principle solution including the acquisition task of technical object and technical relationship was proposed. Based on extensible markup language schema definition (XSD) and unified modeling language (UML), the representation model of patent technical solution was built up. According to the characteristics of mechanical patent’s text, technical object with the method of maximum entropy principle and patent term dictionary was acquired. The composition verb database was established and technical relationship was acquired. This method has some advantages such as the intuitionistic representation of the patent knowledge and the feature that the knowledge was automatically processed by computer. A whole process involved the steps like acquiring the principle knowledge from patent documents, writing the knowledge into XSD and transforming XSD to the representation model was illustrated with a US patent in detail. The model and process laid the foundation for the efficient utilization of patent knowledge.