Being free from drift and intensive error,the digital optic fiber sensors of linear type and angular type can be chosen according to the request of detection.This paper designs a kind of digital optic fiber sensors that relfecting light realize the code reading and recognizing of increment type encoder.We refer double code tracks to response the variations of two directions of left and right (or clockwise and anticlockwise).The analysis illustrates tha the digital optic fiber sensor is free from drift and intensity errors.