Mid-infrared lasers have a lot of potential applications, such as laser medicine, spectroscopy and infrared countermeasures. In order to obtain a compact and potable mid-infrared laser source, a diode-pumped fiber laser emitting at 2.8 μm from a heavily erbium-doped ZrF4-BaF2-LaF3-AlF3-NaF double-clad fiber was demonstrated. A fiber-coupled laser diode centered at 975 nm was coupled into the inner cladding as the pumping source by an achromatic coupling system consisted of two aspheric lenses. The laser cavity was composed of a protected gold mirror butted against the rear end of the active fiber, and the other end with 4% Fresnel reflection. The 2.8 μm lasing was achieved when the launched pump power was higher than 0.37 W. The experimental results indicated that the center wavelength and linewidth of free running were 2.785 μm and 0.9 nm, respectively. Moreover, the maximum output power of the fiber laser working at the transverse-fundamental-mode was 0.98W, corresponding to the slop efficiency of 17%. High efficient watt-level single mode mid-infrared fiber laser was obtained using the efficient energy transfer upconversion processes between Er-Er ions.