Ga-assisted desorption of native surface oxide on GaAs substrate is investigated at low substrate temperature. The progress is monitored by reflection high energy electron diffraction (RHEED), and time dependence of RHEED intensity curves is recorded by a CCD camera. By fitting the curves, the oxide desorption rates are deduced, which depend strongly on the substrate temperature and can be fitted well by Arrhenius relationship. Furthermore, the absorption coefficients of the oxide layer to the high energy electron are estimated. The feasibility of using Ga-assisted desorption for overgrowth is confirmed by growth of high quality low-density InAs quantum dot samples. The result suggests that Ga-assisted desorption is extremely promising for the overgrowth, where a smooth interface is needed to be well preserved.