Underwater self-reconfigurable system(USS),an underwater self-reconfigurable robot consisting of two types of modules,can reform various configurations in real time.Compared with normal underwater robots,its diverse configurations bring forward good adaptability and more abundant gaits.For the tree-like configurations,we propose a technique for dynamic modeling and configuration description.The eel-like configuration and the octopus-like one are chosen as examples to verify the technique,and some gaits are designed.For the eel-like configuration with the serpentine gait,the technique gives the same simulation results as existing eel-like models.For other cases,simulation results are consistent well with what happens in nature.