The invention relates to an LED current driving system. The LED current driving system comprises an LED driver. The LED driver comprises at least one LED driving unit for outputting a driving current to an LED. Each LED driving unit comprises a plurality of current sources and a plurality of switches. The switches are connected to the corresponding current source. Each switch controls the ON/OFF state of the corresponding current source in accordance with the duty cycle control signal and a current control signal. Therefore, by integrating the LED driver on the LCOS panel, the LED current driving system of the invention can decrease the pin number of the LCOS chip, the overall area and the system cost so as to improve the yield of the LED current driving system. Besides, the LED current driving system utilizes the current sources to form the driving current to stably and precisely control the driving current flowing through the corresponding LED so that the color quality of the image can be improved.