It is always using F-P linearity cavity in double-clad fiber lasers. The cavity is composed of one dichroic mirror and fiber end Fresnel reflector (reflectivity nearly 4%). This is a defect and unstable cavity. It cannot exactly select frequency, and the linewidth of the laser is extensive. In some applications requiring wavelength strictly, this kind of laser is limited. As a rule Bragg gratings that compose a laser cavity are fabricated in a high germanosilicate host fiber and then spliced with an Yb3+-doped active fiber. Difference of parameters of the two kinds of fibers leads to additional losses of both pump and signal. A double-clad fiber Bragg grating which was fabricated in the core of Yb3+-doped double-clad fiber using the phase-mask method is reported. This kind of grating is used as the output mirror of the D-shape inner cladding Yb3+-doped double-clad fiber laser, the fiber length is 10 m and 20 m respectively. The laser operating near 1058 nm with stable and narrow-FWHM (3 dB bandwidth is 0.329 nm) is realized. The maximum output power laser is 570 mW. Finally, these experimental results are analyzed theoretically.