Abstract: When systemic functional linguistics is used in natural language generation systems，it needs knowledge representation.Focusing on Penman，this paper finds that a major representation method is the system network.However，this knowledge representation method cannot fully represent the communication goal of language and the organization principle of three meta-functions.Besides，there also exist some technical flaws when it is implemented in computer.Based on this，this paper puts forward two basic ways to improve the system network：the theoretical approach which is based on complex science and the technical approach which is based on artificial intelligence.Through this research，this paper is to develop the communication between systemic functional linguistics and other subjects，thus promoting the linguistic research oriented in natural language processing.