Vertical light-emitting transistor is a kind of optoelectronic devices combining characteristics of light-emitting and the “on/off” function of transistor, and its channel length can be reduced to nanometers to make it operate at low voltages and high speeds. Holes and electrons injected from source and drain electrodes form excitons in the emissive layer and radiate light. The amount of charge carriers can be controlled by the gate voltage, consequently to control the intensity of light emission. In this paper, by inserting a thin hole-transporting BCP layer at different locations in the device ITO/NPB（40nm）/Al（30nm）/NPB（20nm）/Alq3（55nm）/Al, we explored the reasons of large drain current and the detailed carriers processes in the device by studying the variation of their optoelectronic characteristics. Our experimental data confirmed that holes injected from central Al gate contribute to the current in the channel. Further, LiF thin film was used as a buffer layer to modify the drain electrode, in this way to improve electron injection and reduce drain current. As a result, relatively stable light-emitting transistors were obtained with significant enhancement in light emission, and the emission intensity can be controlled by the gate voltage. The color of the emission light can easily be tuned by using different luminescent materials.