Abstract: An expert system of radar radiation-source recognizing based on knowledge library is proposed upon the analysis of the characteristics of radar radiating-source recognizing. The system structure and object-oriented model are discussed in this paper. Data bases (DB) are set up according to system demand, case bases (CB) are established on accumulated cases, rule bases (RB) are established after accepting expert experience, knowledge of this field, and model bases (MB) built according to the structure of knowledge. The four bases are combined in the expert system. The reasoning method based on case, rule and model are described. Comparing with each other, the advantage and disadvantage of these reasoning methods are obtained. The mixed reasoning based on case, rule and model is sussested to overcome their shortcomings. The functions of system and way of realization are described in the paper. It is proved by usage that the expert system of radar radiation-source recognizing based on knowledge base can achieve the same reasoning result as the expert.