Abstract: Recent development and applications of distributed optical fiber stress sensor are described briefly. Based on the theory that coupling coefficient is related to external force, a distributed optical fiber stress sensor is introduced. Distribution of external force is measured by polarization coupling coherence. The principle of location and measuring strength of stress is discussed. The influence of light and polarizer and other things upon the sensitivity and resolving power of the sensor, is discussed. SLD is used as light and proton-exchange LiNbO3 wave-guide is used as polarizer. At the wavelength of 1.3 μm, the resolution of the sensor is better by ±10 cm and its sensitivity is better by 5%.