All-fiber add/drop filters are the key components in fiber communication systems. The Bragg grating assisted mismatched coupler for add/drop filter is not interferometric,easy to fabricate and works stable. The filter is based on 248 nm ultraviolet-written Bragg grating in 2×2 coupler fused with a standard single mode fiber and a self-made high germanium doped photosensitive fiber. The filter with maximum reflectivity about 20 dB,bandwidth about 2 nm is obtained. Filters with big maximum reflectivity and long bandwidth can be obtained by writing chirped Bragg grating on the uniform region of the coupler or writing Bragg grating on the non-uniform region of the coupler.