Aiming at Knowledge reuse and knowledge sharing and solving the problem of inefficiency of knowledge acquisition caused by the knowledge are not structured description,a method of knowledge acquisition based on ontology for CNC machine tools is proposed by studying the Web text in the field of machine tool knowledge and analyzing of text structure features.The original information of the Web text is obtained through the crawler program, and the sentences containing the hyponymy is extracted from the processed Web text information. The Institute of Computing Technology, Chinese Lexical Analysis System (ICTCLAS) is used to carry on the Chinese word segmentation. The concepts can be acquired after segmenting Chinese texts and then the concept set and the concept tree can be generated. At last, the ontology is generated and stored as OWL.In the experiment, the knowledge is extracted from the Web pages which is selected randomly, and the comparison experiment is carried out to prove that the method can obtain the semistructured and structured Web text information in the field of CNC machine tools effectively.