How to reduce secure and repeated replies is a challenging problem in the open-domain multi-turn dialogue model. However, the existing open-domain dialogue models often ignore the guiding role of dialogue objectives and how to introduce and select more accurate knowledge information in dialogue history and dialogue objectives. Based on these phenomena, this study proposes a multi-turn dialogue model based on knowledge enhancement. Firstly, the model replaces the notional words in the dialogue history with semaphores and domain words, so as to eliminate ambiguity and enrich the dialogue text representation. Then, the knowledge-enhanced dialogue history and expanded triplet world knowledge are effectively integrated into the knowledge management and knowledge copy modules, so as to integrate information of knowledge, vocabularies, dialogue history, and dialogue objectives and generate diverse responses. The experimental results and visualization on two international benchmark open-domain Chinese dialogue corpora verify the effectiveness of the proposed model in both automatic evaluation and human judgment.