A curvature sensor based on fiber ring laser is reported in this paper .The Sagnac loop based on single-mode-polarization-maintaining-single-mode is i nserted into a fiber ring laser served as the curvature sensing element and the filter.The spectrum of the Sagnac loop is modulated by the curvature,which for med a curvature tunable filter in the laser cavity.The intracavitary fiber ring laser is used to narrow the corresponding 3dB bandwidth and enhance the resol u tion of the curvature sensor.The curvature will be measured by detecting the ou tput power of this system.The working mechanism of the sensing system is analyz ed theoretically,and the feasibility of the high-resolution curvature sensor i s verified through experiments.The experimental results show that the highest cu rvature resolution of 6.5×10－8 m－1 is obtained within the curvatu re range from 0m－1 to 5.6865m－1.With the method based on in tracavity sensing,the curvature resolution level of the sensing system has been improved from 10－4 m －1 to 10－8 m－1.At the same time,the system stability and measurement error are measu red i n the experiment.Due to its advantages of simple structure,easy to manufacture and low cost,the sensor has a potential application prospect in the field of b uilding structure health monitoring and micro-bending angle measurement.