We model and derive an algorithm for the assort-packing and distribution problem (APDP) in the fashion apparel industry. Assort-packing is a common method used to reduce the distribution lead time between manufacturers and retailers, wherein different items are packed together in one box according to the retailers’ demands. Specifically, in the fashion industry, multiple box types are configured by varying the size distribution of the same apparel product. In this study, we propose an optimisation model to quantitatively solve the APDP with respect to how many box types should be configured, how to configure the size distribution in each box, and how many of each type of box should be sent to stores. In particular, the modelling and algorithm development focus on the size-assorted homogeneous-article configuration in the APDP, a widely used assort-packing method in the fashion industry. We show that the APDP is NP-hard, and propose a heuristic algorithm in which a pre-processing step significantly reduces the search space. Numerical studies of the industry scale are conducted and show that the algorithm outperforms the benchmarking algorithms.