This paper establishes a uniform kinematics model to describe the undulation surfaces by the long flexible fin of Gymnarchus niloticus, with various factors comprehensively considered. Simulation is carried out using the morphological measured data and some simplified hypotheses to related factors. Compared with the filmed views, the simulation results show that the kinematics model can effectively depict the movement curved faces of the long flexible fin, and has better adaptability as well as versatility. Meaningfully, the establishment of the kinematics model for the long flexible fin has made a good preparation for further finite-element-based dynamic analysis.