基于耦合模理论及传输矩阵法，给出了级联长周期光纤光栅和Bragg光纤光栅系统(CLBG)的耦合模方程与总传输矩阵，理论模拟了CLBG的反射谱，得到的反射峰位置与已知文献中所给出的两个反射峰的位置关系相吻合。在此基础上，模拟了镀膜CLBG之间的光纤长度、薄膜折射率、薄膜厚度等参数对反射谱的影响。由仿真结果可知，CLBG反射峰中受长周期光纤光栅和Bragg光纤光栅共同影响产生的反射峰对外界环境的变化非常敏感，其对薄膜折射率的分辨率较单个镀膜长周期光纤光栅高2个数量级，表明CLBG在薄膜传感领域具有重要的应用价值。

Based on coupled-mode theory and transfer matrix method, the general transfer matrix for evaluating cascaded long-period grating and fiber Bragg grating system (CLBG) is obtained. Through general transfer matrix, the reflection spectrum of CLBG is simulated, and the theoretical simulations agree well with the relationship of two reflected peaks given in the known paper. Effects of the length of fiber between long-period fiber grating (LPG) and fiber Bragg grating (FBG), film refractive index and thickness on coated CLPG are discussed. From simulation results, reflection peaks affected by LPG and FBG in CLBG are sensitive to changes of the film parameters, and resolution on the film refractive index is 2 orders of magnitude higher than that of single coated LPG, which shows that coated CLBG has important application value in sensing field.