To leverage the advantages of both template-based and templatefree methods and suppress their drawbacks simultaneously, semitemplate methods decompose the retrosynthesis process into two steps: i) identifying the reaction center in the given product and obtaining synthons accordingly , and ii) completing the synthons in an autoregressive or non-autoregressive way. The synthons work as the "semi-templates", which provide reliable molecular fragments for generating reactants. Given a synthon, G2G adds atoms step by step, and GraphRetro adds the clusters of atoms instead. MEGAN defines five kinds of graph actions in advance to complete synthons. Besides generating molecular graphs conditioned on synthons, RetroXpert formulated the synthon completion process as a Seq2Seq model. However, the above methods do not consider jointly leveraging the atom-level and motif-level information of the synthons.