In this paper, the principle of fiber-optic interferometric compliant cylinder sensor is analyzed from the perspective of energy distribution, and the compound compliant cylinder calculation formula of the equivalent stiffness coefficient is given. Finite element analysis method is used to simulate the natural frequency of the compound compliant cylinder, and the simulation results show that the distance from wrapped position of the fiber-optic to the intermediate inertia oscillator should be 5 mm. In the experiment, the natural frequency measurement method is used to indirectly calculate the equivalent compliant cylinder stiffness coefficient. The experimental results from the measurement of three different compliant cylinder sensors show that the proposed method can be used as the basis of the calculation of the compliant stiffness coefficient.