Abstract: In engineering measurement, it is necessary to input the corresponding strain coefficient of distributed armored optical fiber for engineering monitoring, but many manufactures do not provide relevant parameters. Based on the principle of distributed sensing system of Brillouin optical time domain analysis, a strain coefficient measuring device for distributed armored optical fiber was developed. Compared with the traditional measurement of optical fiber strain coefficient, the innovation of the device lies in proposing and realizing an interval calibration method, which avoids the interference caused by fixture during the process of stretching the fiber. In this paper, the developed device was used to measure the strain coefficient of armored optical fiber from two manufacturers. The research results show that the interval calibration method can obtain more accurate measurement results than traditional methods.