GaAs single crystal is one of the main substrate materials for optoelectronic devices, and has important applications in infrared LED. However, its high impurity concentration and low carrier mobility seriously restrict the performance of infrared LED devices. To obtain silicon doped GaAs single crystals prepared by vertical gradient freeze (VGF) method with low impurity concentration, high mobility, uniform carrier distribution and high utilization ratio, the influences of thermal field distribution, materials of synthetic boat and furnace, and process parameters on crystal quality, impurity concentration, mobility and carrier distribution of single crystal were studied in this paper. CGSim software was used to conduct numerical simulation research on the thermal field system of single crystal growth thermal field. When the length ratio from temperature zone 1 to temperature zone 6 is 8∶12∶9∶5∶5∶7, the constant temperature zone reaches the longest, the dislocation density is below 1 000 cm-2, and the crystallization rate reaches 85%. With GaAs polycrystalline synthesized by roughening quartz synthesis boat, and the mullite furnace replacing the quartz furnace, GaAs single crystals with overall mobility higher than 3 000 cm2/(V·s) were obtained. The process parameters of single crystal growth were studied. The axial carrier concentration uniformity of single crystal is improved by increasing the head pulling speed and decreasing the tail pulling speed, by which the carrier concentration difference between the head and tail is reduced by 33%, and the tail mobility increase from 2 900 cm2/(V·s) to 3 560 cm2/(V·s). The effective utilization length of single crystal gains increase by 33%, and the utilization rate of single crystal reaches 75%, which greatly reduces the raw material consumption cost.