Abstract: In this paper, the intrinsic self-regulation effect of the arc in the MIG一welding of aluminium in argon, its physical essence, the raechanism and affecting factors have been investigated. Curves of the melting rate by different arc length are measured with an arc demonstrator. Three types of power sources, i.e. CP, CC and CAC, and the corresponding charateristic curves of the melting rate are discussed in detail. From the result of testing it shows that the most strong intrinsic self-regulation effect appeared in the upper part of the curves in the short circuiting transfer range. This phenomenon has been accounted for the change of metal transfer mode and the size of the metal droplets (short circuiting frequency). In this paper, the formula and the time constant of the arc length recovered by the intrinsic self-regulation effect of the arc and by self-regulation effect of the arc and both regulation effect of the arc were discussed as well.With the power source of CAC and the wire feeding system of constant speed, the stable region of the arc by pure aluminium wire of 1.6mm diameter and centralized regulation charateristics curves were evaluated.It proves that the intrinsic self-regulation of the arc in the MIG-welding of aluminium in argon is sensitive enough to adjust the process of welding and facilitate the arc stability, the process of welding with this effect has the advantage in getting the arc stability, uniform penetration and good bead pattern.