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.