2.1 μm GaInSb/AlGaAsSb double quantum well lasers were reported. With optimization of epitaxial design and ohmic contact, these uncoated broad-area lasers exhibited a maximum power conversion efficiency of 9.8% which was 1.5 times greater than previous value, a room temperature continuous wave output power of 615 mW and a pulsed wave output power of 1.5 W were achieved. The threshold current density of these lasers was as low as 126 A/cm2, and the slope efficiency was as high as 0.3 W/A. By testing lasers with different cavity lengths, the internal loss and the internal quantum efficiency were measured as 6 cm-1 and 75.5%, respectively, which were all improved compared with previous device. The output power of laser diode operated in CW mode shows no apparent degradation after 3 000 h.