In this paper, the dynamic characteristics of an inflatable manipulator based on the potential field was explored. To this end, a elephant trunk-like inflatable soft manipulator is designed and its dynamic modelling analysis is explored. First of all, the mechanical structure is designed based on the principle of using different elastic materials under the same stress and causing the local strain difference to make the material bend. Then, based on the Yeoh model, the strain energy density function of the superelastic material is established. By calculating the elastic potential energy as well as the gravitational potential energy of the soft manipulator, and using the Lagrange method, the general equation of dynamics is obtained. Finally, different envelope space is obtained by changing the pressure value of the inner cavity by bending. The results show that the stress uniformity can be applied to the non-destructive gripping operation condition.