A watt-level 100-nm tunable 2.8 μm-band mid-infrared fiber laser is demonstrated. By employing a blazing grating as the feedback, output power exceeding 1 W, tuning range of higher than 100 nm from heavi ly Er3+-doped ZBLAN double-clad fiber pumped by a laser-diode centered at 975 nm is obtained in continuous wave regime. Output power at 2.831 μm of the fiber laser is 1.02 W corresponding to the slope efficiency as high as 21.6%.