The theoretical and experimental research based on the oblique apodized fiber Bragg gratings (FBG) is carried out, in order to solve the crosstalk to the main peak from the high reflected sidelobe of the uniform fiber Bragg gratings written by femtosecond laser point-by-point. According to the characteristics of the refractive index induced by femtosecond laser, the AC coupling coefficient in the coupled mode model is modified. The apodization type of the oblique apodization method is verified to be Gaussian by finite element simulation. Then the key parameters affecting the apodization effect are studied experimentally. The results show that the experimental results are basically consistent with the simulation results, and when the initial lateral displacement is between 5 μm and 10 μm and the asymmetric offset is less than ± 2 μm, the side mode suppression ratio can be improved to 15 dB. The research results provide important theoretical support and practical guidance for improving the side mode suppression ratio, and are of great significance for promoting the development of fabrication technology of FBG.