A new kind of optical fiber sensor, transmission moving-grating optical fiber sensor is presented. Optical fiber is used as light-transmitting element in this kind of sensor. Sensitive element is a couple of equal pitch gratings, the one is a fixed grating, the other is a moving grating. Light flux changes as the position of the two gratings change, then after transformed by the photoelectric conversion system, the signals are output as electronic signals. Because of its simple structure and convenient operating, this kind of sensor can be used to measure displacement, strain and other physical quantities. Theoretical analysis of this sensor and experiment results of displacement measurement are provided in this paper. The results indicate that theoretical analysis is identical with experiment results and the sensor has a certain measuring sensitivity.