Laser diode is a current injected device and the performance of current supply has great impact on the characteristic and life of LD.A current supply for high power LD is designed by the chip LT3755，and the output current can be changed continuously from 3.3A to 5.6A.When the output current is 4.5A，the current variation obtained in an experiment within 3 hours are smaller than 2mA，and the current stability is 4×10-4.In addition，the power supply has also some good features such as undervoltage protection，overvoltage，overcurrent，soft startup and other functions.