Abstract: An assembly job shop produces assembly products with multiple specifications and in small batches. Assembly products usually have diversified BOM (Bill of Material) structures, which are made up of customized parts, but products with the same specification still include a certain proportion of shared parts, which respectively have certain batch sizes. Lot splitting scheduling in an assembly job shop requires optimized batch partitions and subbatch sequencing for assembly parts. The high delivery reliability of customers is considered, and a mathematical model established for lot splitting-scheduling, and a hybrid algorithm based on genetic algorithm and priority dispatching rules proposed to solve the mathematical model. Finally, the effectiveness of the proposed hybrid algorithm is validated by a simulation experiment.