A 1570 nm single-wavelength fiber laser based on fiber Bragg grating (FBG) with direct emission was demonstrated in this work. A Sagnac broadband reflector composed of fiber coupler and a output coupler composed of a partial reflection FBG were used to build a straight cavity fiber laser. By optimizing the reflectivity of the FBG and output direction, the highest resonant efficiency of 24.42% was realized with the maximum output power of 2.834 W and the side mode suppression ratio of 65 dB. By increasingthe cavity length to increase the number of resonant longitudinal modes, the stable beat-free laser emission of 1570 nm single wavelength fiber laser was obtained based on the average effect among the longitudinal modes. And then, the passively mode-locked output of 2 μm-band fiber laser was realized by utilizing the 1570 nm fiber laser as the pump source of thulium-doped fiber.