The soft actuator has a high degree of flexibility and good adaptability, and has great development potential in the fields of medical care, rescue, service, and manufacturing. At this stage, the deformation types of the soft actuator are mainly bending, expansion and contraction, which limits the flexibility of the soft actuator. In order to improve the operating of the soft actuator, a new type of helical deformation soft actuator is proposed. The soft actuator is driven by the pulling cable, and the helical deformation is limited by the scaffold. The soft actuator end can move controllably in three-dimensional space. Based on the kinematics theory of constant curvature continuous robot and the geometric relationship of helical deformation, a kinematic model for constant curvature helical deformation is developed to obtain the coordinate transformation matrix of the actuator end in the global coordinate. Through simulation and experimental data comparison, the model accuracy is greater than 98%. An accurate kinematics model for the helical deformation soft actuator is presented, and provides a theoretical model basis for the construction of the ultra-high flexibility gripper based on this actuator in the future.