Based on the femtosecond laser inscribing technology and side-pump coupling technology, a kilowatt-level monolithic all-fiber laser oscillator without fusion splice in the main optical path is obtained. In addition, a pair of fiber Bragg gratings are written in a large-mode-area and double-cladding ytterbium-doped fiber by combining femtosecond laser and phase mask, so as to form a resonant cavity. Meanwhile, two side-pump couplers are fabricated by tapered-fused technology in the same ytterbium-doped fiber. With a semiconductor laser of 976 nm as the pump source, the maximum output power of 1052 W is obtained at a center wavelength of 1070 nm, and the optical-optical conversion efficiency and the beam qualityfactor M² are about 73% and 1.8, respectively. A compact and stable monolithic fiber laser oscillator system is presented, and its potential in realizing laser output with high power and high beam quality is demonstrated, which is of great value to the development and application of high-power fiber lasers.