The soft surgical manipulator is the scientific frontier and research hotspot in the field of minimally invasive surgery and robotics, which is very important to improve the level of minimally invasive surgery. The existing sensing methods, such as vision, electronics and photoelectricity, have not solved the problem of measuring the state of the arm of soft gymnastics. The optical fiber sensor arranged in a straight line in the soft manipulator is easily broken and repeatable when the flexible manipulator is stretched and bent. Problems such as poor sex, failed to achieve closed-loop control of the surgical manipulator, limiting its surgical application.Therefore, a state measurement method of soft manipulator based on helical optical fiber sensor was proposed, and its sensing characteristics were studied. Different from the linear optical fiber sensor method, the unique helical structure could prevent the sensor from dislocation and support the ductility of the material, which was convenient to meet the measurement requirements of the operating arm when it moved. Based on the theoretical analysis of the movement characteristics of the expansion and bending of the pneumatic soft maniputator, the sensing model of the helical fiber grating in the soft maniputator was established by using the FBG sensing points engraved on the optical fiber, and the relationship between the center wavelength drift of the FBG and the bending curvature of the soft maniputator was deduced. Finally, in order to verify the sensing performance of the helical fiber grating in the soft manipulator, the sensitivity and stability of the sensing were tested. The experimental results show that the helical optical fiber sensing method proposed can realize the state measurement when the manipulator is extended by 10% and the bending angle reaches 180°. The error between the theoretical bending angle of the manipulator and the optical fiber sensing is up to 9%, and the sensing sensitivity is up to 12.55 pm/(°) which can meet the needs of the measurement when the soft maniputator is retracted and bent in all directions.