Based on the theory of fiber Bragg gratings and in response to the application requirements of narrowband filters for 2?μm band lasers, this paper designs a raised?cosine apodized fiber grating filter. The effects of different flatness coefficients and modulation depths on the 3 dB bandwidth and side lobe suppression ratio of the grating reflection spectrum are systematically analyzed through simulations. To achieve both narrowband filtering and high side?lobe suppression, a cascaded grating structure is adopted for optimization, and further shaping of the reflection spectrum is realized by adjusting the inter?stage parameters. The final optimized cascaded grating filter exhibits a narrow 3?dB bandwidth of 0.18 nm and a side?lobe suppression ratio better than 20 in the 2?μm band, which validates the feasibility and superiority of combining raised?cosine apodization with cascading technology for filter design in the 2?μm wavelength region.