Abstract: In response to low space utilization in traditional plane warehouses and the high costs associated with converting them into automated storage and retrieval systems (AS/RS), a study is conducted on a puzzle-based storage system (PBS system) suitable for the transformation of plane warehouses. This system aims to maximize warehouse space utilization while ensuring high picking efficiency. To address the complexity of the retrieval process inherent in a PBS system, an algorithm for diagonal optimal picking paths based on useful points is proposed. This algorithm utilize a useful point movement strategy according to the locations of goods to enhance computational efficiency, thereby reducing the number of picking movements and the operation time. Results indicate that the proposed method can achieve the shortest picking time for single items, single empty slots, and any storage location within milliseconds. Comparative analysis with other algorithms reveals that the proposed algorithm has significant advantages in terms of solution efficiency and stability of the optimal number of picking steps. Analysis of actual application cases confirms that the space utilization of plane warehouses increases by 100% after transformation based on PBS systems, demonstrating its practical value.