A near single-mode 1.2 kW all-fiber laser oscillator with optical-optical efficiency of 70.8% and beam quality of M■■≈1.03, M■■≈1.55 was reported. The laser is bidirectional pumped by laser diodes with locked wavelength of 976 nm. Therefore, the fiber laser takes on nearly linear output power versus pump power from threshold current to full current, and the instability capacity of output power is less than 2% during 8 h operation. The laser can be operated within wide temperature scope, the excellent temperature uniformity is shown on temperature cycle test.