Bragg gratings are used in various applications including optical communication systems and sensors. The influencing parameters of the reflectivity of Bragg gratings hold significant importance in the research ofoptical sensors. Both domestically and internationally, there exist various external parameters including vibration sensing characteris temperature sensing characteristics and lateral force characteristics of fiber gratings. However, the comprehensive exploration on how these external parameters impact the fiber grating is insufficient. Thus, it is crucial to delve into the internal characteristics of waveguide gratings. This paper investigates the transmission characteristics of electromagnetic waves inwaveguide gratings by changing internal parameters.The Bragg grating is taken as an example in this paper to derive the coupling mode equation of the grating from the wave equation of the light field, and then the 2×2 matrix characterizing the grating characteristics is reproduced by solving the coupling mode equation and applied to a matrix derivation that can characterize the characteristics of the sampling grating. The formula of the equations is deduced, and a simplified formulation linking the reflection coefficient to the grating length, effective refractive index, and coupling intensity is obtained. For uniform Bragg grating and sampling grating, the influence of parameters on their reflectance spectrum and transmission spectrum was studied by MATLAB numerical simulation method. As the influential factors, the grating length, effective refractive index, coupling intensity, grating segment length, blank segment length and grating period are included. The numerical simulation spectrum and experimental results are also givenThe results demonstrate that, for the uniform Bragg grating, as the length of the grating segment increases, both the reflectance peaks in the reflection spectrum and transmission spectrum exhibit an upward; a decrease in effective refractive index leadsto a blue shift in the position of both reflection and transmission spectra; an increase in coupling intensity results in higher reflectance peak heights and wider spectral widths. For the sampling grating, the increase in the length of the grating segment leads to an increase in the coupling intensity of the sampling grating, resulting in a wider interval between the reflection peaks; the length of the blank segment increased, while the reflection peaks at all levels remained unchanged and there is a decrease in the spacing between the reflection peaks; the increase in the number of grating periods leads to a longer transmission distance of the light field within the grating, resulting in an increased number of backward transmissions and enhanced intensity of reflection peaks at all levels in the reflection spectrum.The simulation analysis presented in our work offers theoretical support for the preparation and design of target gratings in various applications, such as FBG sensing, distributed Bragg feedback (DBR) lasers and grating filters.