Abstract: Aimed at the problems of arc length control in pulsed MIG welding power supply,the research of arc self-regulating mechanism and arc adjusting mechanism under the control of the pulse frequency modulation (PFM) was developed.The mathematical model of arc length was established.The principle of PFM arc adjustment system was introduced and the PFM current regulation model was given.The PFM arc control mechanism and the problems existing in the arc control were analyzed for non-resistance wire and resistance wire.A more stable welding effect can be obtained for PFM current regulation of non-resistance wire from theoretical derivation.For the resistance wire, the stable welding effect can be obtained when CTWD is fixed and satisfactory welding results cannot be obtained while CTWD changing.Finally the step tests of PFM arc adjustment were carried out by using non-resistance wire and resistance wire,respectively.The theory above is verified by test results.