Eco-efficiency has been proved as one of the powerful indicators in link with environment management and economic output. As a core procedure of remanufacturing activities, upgrading the eco-efficiency of remanufacturing process planning is of great significance for maximizing the circular economic advantages of remanufacturing. With the increasing of individual differences in used parts, the remanufacturing process planning is becoming more complicated. In this paper, a knowledge-based method for remanufacturing process planning is proposed as part of the efforts in upgrading eco-efficiency which also aims to improve the efficiency of process planning and realize the inheritance and evolvability of the process planning knowledge. Based on the identification of basic attribute characteristics and damage characteristics of used parts, a similarity calculation method is presented to match the most relevant historical remanufacturing process planning knowledge from the existing knowledge base, so as to design the feasible initial process plan set. For eco-efficiency upgrading, a remanufacturing process planning model is proposed to obtain the process plan with the optimal economic and environmental performance, and then the knowledge base can be updated and expanded. Finally, a case study of remanufacturing a used worm gear is demonstrated to validate the proposed method.