根据理想模展开下的耦合模方程，对光纤布拉格光栅的峰值反射率公式进行了数学推导，得到了布拉格光纤光栅的光谱反射率表达式。全面讨论了光栅周期、光纤栅长、光致折射率微扰最大值等参数与光纤光栅反射光谱的关系。仿真结果显示了固定参数下布拉格光栅的极限窄带宽，得到的反射率为1、带宽为0．02nm的窄带宽布拉格光栅，比现今分布式传感系统中使用的布拉格光栅的带宽窄1个数量级。这种布拉格光纤光栅用于分布式传感系统，可大大提高分布式传感系统中光源的带宽利用率，消除各信号间的相互串扰，提高传感光栅复用数目，降低解调系统成本。

According to the ideal approximation of the coupled-mode theory,the Bragg equation and the peak reflectivity expression of the fiber Bragg grating are derived. The relationship between the grating spacing,the grating length,the max of refractive index micro-disturbance and the reflectivity is analyzed. The simulation result shows the least narrow bandwidth of Bragg grating under the defined parameters is 0.02 nm when its reflectivity is 1,which is much narrower than the fiber Bragg grating used in typical distributed sensor system. It is proved that this fiber Bragg grating can be used as a fiber grating sensor for distributed demodulation system,which will improve the bandwidth availability of light source in the distributed sensing systems,increase the number of sensing Bragg gratings,eliminate the cross-effect between signals,and reduce the cost of the demodulation system.