The optical frequency domain reflectometer (OFDR) boasts distributed sensing capabilities, including high spatial resolution, precision, and sensitivity. This technology exhibits significant promise across diverse applications, ranging from oil and gas resource exploration to structural health monitoring and minimally invasive medical intervention surgery. Despite its merits, challenges such as sweep frequency nonlinear noise, coherent fading noise, and weak Rayleigh backscatter signals in optical fibers can impact the performance of optical frequency domain reflectors. This article elucidates the fundamental principles of optical frequency domain reflectors and expounds on two sensing demodulation methods: wavelength and phase. Additionally, it delves into various strategies for mitigating sweep frequency nonlinear noise and coherent fading noise. The discussion extends to the progress in sensing applications of optical frequency domain reflectors, encompassing three-dimensional shape, large strain, high temperature, refractive index, and other pertinent aspects.