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.