Abstract: Digital welding power source becomes more and more complex,and the conventional program system can't meet the needs.Muti-tasks program system on welding power source was developed using uC/OS-ii.Structure of uC/OS-ii and multi-tasks was described,and the method to create tasks reasonably according to the function of the power source's software system was presented.Running process of the program was demonstrated by sending and receiving in serial communication.At last,pulsed current on resistance load experiments indicated that uC/OS-ii can work stably on digital power source and improve the dynamic characteristic of welding equipment.