Abstract: After analyzing the characteristics of directed-connectors, a uniform representation of parts is presented and the directed-connector knowledge is exploited for assembly sequence planning. By integrating geometry-based reasoning with knowledge-based reasoning, the computation complexity is reduced drastically and the assembly sequences obtained are more feasible and practical. In addition, Free Space Graph is defined and its attributes are discussed. With the help of Free Space Graphs, the approach can solve the problem of non-monotone assembly sequence planning successfully.