A BUCK-type constant-current power is designed. Firstly, the schematic diagram of the power supply is designed and analyzed. Secondly, the circuit is simulated and analyzed based on Saber，and the simulation and experiment results are compared. Finally, for the experimental requirements of input characteristics (with the load constant), the value of the AC input voltage is altered and the change of the current is analyzed. The results show that the current keeps constant when the AC input voltage changes.