Fiber laser oscillators play a vital role in industrial processing, national defense research and other fields. Traditional high power fiber oscillator lasers can only achieve unidirectional output, which is determined by the resonator structure. We propose a new structure that is simple and compatible with the ordinary fiber laser oscillator, which can achieve double high power laser output with only one resonant cavity. Typically, the resonant cavity of all-fiber laser oscillator contains a high-reflectivity grating and a low-reflectivity grating. Briefly, by replacing the high inverse grating with a low inverse grating, the unidirectional output laser oscillator can be converted into a b-directional output laser oscillator. It is suitable for applications that do not require high power and can have multiple lasers working at the same time, because of the smaller size and lower cost. We select a double-cladding Yb-doped fiber with 25/400 μm core/cladding diameter. The length of fiber is 35 m and its absorption coefficient is 0.33 dB/m at the wavelength of 915 nm. By means of bi-directionally pumping with 981 nm laser diodes, the maximum output power at both ends is 2871W and 2666 W respectively. We believe that with the further study of stimulated Raman scattering and transverse mode instability, bidirectional output lasers can achieve higher power outputs.