A soft gripper whose whole body is made of some soft materials has a possibility to manipulate arbitrarily shaped objects by adapting its shape. The present soft gripper has just been being expected to be utilized in a simple task such as just grasp and release because an accurate control of the shape and grasping force is difficult due to its softness. However, in order to utilize it in wider situations than the present expected situations that it would be utilized, not only such a binary control but also accurate control of its shape and contact forces would be necessary to realize dexterous manipulation tasks. In order to realize such dexterous manipulation, developing a plausible model is important. In this paper, dynamic models of a soft gripper which is driven by one cable are proposed. The proposed models are based on a spring-mass model that is simple but can express the movement of the proposed soft gripper enough. Several identification experiments according to the proposed models are performed using an experimental setup.