The invention provides a method for controlling surface granularity of a GaSb monocrystal substrate. The method comprises the steps that firstly, a GaSb monocrystal wafer is polished, and after being polished, the GaSb monocrystal wafer is soaked in absolute ethyl alcohol; secondly, the GaSb monocrystal wafer is subjected to ultrasonic cleaning in absolute ethyl alcohol, petroleum ether and an isopropanol organic solvent in sequence, the cleaning time is 10-15 minutes in each kind of reagent, and after cleaning is completed, the GaSb monocrystal wafer is soaked in absolute ethyl alcohol; thirdly, the GaSb monocrystal wafer is soaked in a solution obtained by mixing hydrochloric acid and isopropanol according to the volume ratio of 1:4 to be subjected to ultrasonic leaning for 5-10 minutes, and after ultrasonic cleaning is completed, the GaSb monocrystal wafer is soaked in absolute ethyl alcohol; fourthly, the GaSb monocrystal wafer is taken out and blown-dry under the nitrogen or inert gas environment, and packing and sealing are carried out. By means of the improved process, the wafer is processed under an ultraclean environment, residual impurities and particles on the surface of the GaSb monocrystal can be effectively removed through the chemical cleaning and nitrogen packing process, the granularity is controlled to be 100/cm<2> or lower, and the surface quality of the GaSb monocrystal substrate is greatly improved.