Indium droplets were grown on GaAs(001) substrates by droplet epitaxy method. The samples grown at different temperatures were characterized by atomic force microscope (AFM), and the surface morphology was observed. The study illustrates that indium droplets are very sensitive to the substrate temperature. The droplet density decreases with the increase of the substrate temperature, and its size increases with the increase of the substrate temperature. The physical mechanism of indium droplet formation at different substrate temperatures was analyzed, and the reason was explained. According to the relationship between the maximal cluster density and substrate temperature in nucleation theory, the functional relationship between the density of indium droplets and the substrate temperature is calculated as nx=5.17 exp(0.69 eV/kT).