Compared with the traditional strain gage and fiber grating sensor, the distributed optical fiber sensor has the remarkable characteristic of distributed measurement and has become the research hotspot in the field of sensors. With the progress of technology, the optical frequency domain reflectometry (OFDR) technology based on Rayleigh scattering has been developed rapidly. The measuring principle of OFDR is introduced and the distributed optical fiber sensor is applied to the spiral case model test. In order to test the deformation law of the spiral case after water filling, the overall safety and design rationality of the spiral case and concrete have been checked, and the external concrete strain during the test has been monitored. Through the strain generated by the distributed optical fiber sensor under each level of water pressure loading, the external deformation of the spiral case model and the development of cracks are obtained. The experimental results show that the distributed optical fiber sensor can truly reflect the strain distribution of the structure, timely and accurately monitor the deformation and cracking of the spiral case model under the action of pressure, and identify the damage of the structure.