As a direct bandgap semiconductor with high electron mobility, GaAs and its photoelectric response have been the focus of academic researches. Macroscopic finite element methods combined with semi-classical theory are normally used to simulate the photoelectric response of semiconductor devices with specific structures. With the miniaturization of devices, the microscopic structural features become more important. In this paper, the non-equilibrium Green’s function method with density functional theory(NEGF-DFT) was firstly adopted to calculate the light response of GaAs nanojunctions under chemical doping and gate voltage, and qualitative analysis of the doping density on light response is achieved. This work casts light on the first-principle analysis of photoelectric response of semiconductor devices and will be meaningful to the future researches in this field.