By introducing the grating refractive modulation into the evanescent field coupling,the unified coupled-mode equation for all kinds of fiber grating filters written in fiber coupler is obtained,which parameters have specific physical meaning. The filtering response of three kinds of fiber grating filters written in fiber coupler are analyed by numerical methed of Broyden and shooting. The influences of relative parameters on the filtering response characteristics are investigated theoretically. Drop channel efficiency of 95%,85% and 99% can be obtained for grating assisted coupler,grating reflection coupler and grating frustrate coupler by optimizing parameters. Grating assisted coupler and grating reflection coupler are fabricated with reflectivity 15 and 18 dB.