In order to shorten design period and improve design efficiency of the grab to rapid response to market demands, modular design for the crane grab is one of the effective methods to enhance design efficiency. The design structure matrix (DSM) was used as a tool to capture the physical relationships between components within the grab and DBSCAN (Density-Based Spatial Clustering of Applications with Noise) algorithm was used to cluster the components into modules. A method of module partition DBSCAN-based for product design was proposed, which considered asymmetric relationship between components and association relationship between two modules. The rule of modularity metric was to maximise high cohesion degree within the modules and minimise coupling degree between the modules.