In order to realize the bending stress of gear measurement, based on the analysis of Fiber Bragg Grating (FBG) strain sensing model, an optical fiber dynamic testing system design scheme of gear bending stress was put forward. And then the coupled mode theory was used to analyze the spectrum characteristics of FBG, according to which the optical fiber grating sensor parameter was determined. Based on gear bending stress distribution rule, the set of optical fiber probe and its transmission way were designed. What’s more, the fiber grating demodulation system was designed based on F-P filter. The simulation results verified the effectiveness and rationality of demodulation system. Finally, verified by theoretical analysis, the measurement scheme has the advantages of simple structure, resistance to electromagnetic interference, suitable for distributed measurement, etc.