The modelling method of dynamic flow path feature (DFPF) is proposed for the design process of hydraulic manifold block (HMB). In this method, temporary body model and B-Rep model are adopted to represent geometric model of DFPF; the former is used for showing flow path, checking connectivity and safe wall thickness, and the latter is used for saving the final results. A novel feature topological representation method based on solid adjacency graph (SAG) is provided, and then validity of feature semantics can be checked through SAG. Finally dynamic topological changeability of flow path feature is realized by constraint solution and knowledge driving. Object-oriented model of DFPF is given, and the design process of HMB based on DFPF is illustrated.