2 μm~5 μm GaSb-based VCSEL is an ideal light source for atmospheric detection. However, the im-maturity of its fabrication technology seriously hinders its development. The undercutting effect is the outstanding etch problem in its fabrication. In this paper, Etching characteristics of GaSb is investigated in detail by use of phosphoric acid plus tartaric acid solution. In order to compare them, we chose concentration ratio of H3PO4:H2O2:C4H6O6:H2O as 1 mL: 1 mL: 0.3 g: 10 mL, 1 mL: 1 mL: 0.6 g: 10 mL, and 1 mL: 1 mL: 1 g: 10 mL, re-spectively. The testing results from step profiler and scanning electron microscopy (SEM) were compared and analyzed. Etched GaSb in the solution with a concentration ratio of H3PO4:H2O2:C4H6O6:H2O=1:1:0.6:10 shows very good morphology. Undercutting effect was eliminated and a vertical side wall was obtained with no lateral etching. Etching rate is 0.62 μm/min. The perfect etch behavior of GaSb provides a good technical support for laser preparation.