Abstract: Bias current exerts influence on the LED performance parameters including the internal temperature, junction resistance, and the carrier concentration, which has an effect on frequency response. In this paper, the influence mechanism of bias current on frequency response was analyzed, and the influence trend of DC bias on modulation bandwidth was researched and tested. The results demonstrate that the bias current is basically linearly proportional to the modulation bandwidth while LED's (red, green or blue) working power is less than the rated power. When the working power is close to or exceeds the rated power, the modulation bandwidth will change slowly and eventually stabilizes. With respect to phosphor LED, the bias current has almost no effect on it. This study may provide reference for the selection of bias current and the design of equalization circuit in visible light communication system.