We report a GaSb-based type-Ⅰ quantum well cascade diode laser emitting at nearly 2-μm wavelength.The recycling of carriers is realized by the gradient A1GaAsSb barrier and chirped GaSb/A1Sb/InAs electron injector.The growth of quaternary digital alloy with a gradually changed composition by short-period superlattices is introduced in detail in this paper.And the quantum well cascade laser with 100-μm-wide,2-mm-long ridge generates an about continuous-wave output of 0.8 W at room temperature.The characteristic temperature To is estimated at above 60 K.