Abstract: Constant current LED driver circuit was designed based on CSMC 0.55μm BCD process. Three methods were given for the constant current driver used of MOS saturation constant and current negative feedback structure. Compared the operating voltage of constant current final structure was established. It can effectively reduce the operating voltage and control the current by external resistor and this can be used for LED display. The driving current range of 14.5mA to 91.5mA and it can be enable controlled by the external PWM signal with 7ns respond time. Simulated by Hspice software, the driving current′s variance can be controlled within 1.85% when the 5V supply voltage change in ±10% and it changed 2.14% when ambient temperature changed from 25 ℃ to 85 ℃. Driving current changed less than 5.5% when external voltage varied form 0V to 5V. The operating voltage achieved only 0.38V when the current was 91.5mA.