The invention relates to a melt mixing mechanism for a PVC thermal shrinkage film. The melt mixing mechanism comprises an extruder, a film blowing machine head, and a static mixer which is arranged between the extruder and the film blowing machine head, wherein one end of the static mixer is in combination connection with a screw head part of the extruder, and the other end of the static mixer is connected with a connecting section of the film blowing machine head through a flange; the static mixer is composed of a plurality of twisting elements which are connected in series and are in contact with each other; the plurality of twisting elements are fixedly arranged in a barrel of the extruder. According to the melt mixing mechanism for the PVC thermal shrinkage film, material flows in a gyring manner relative to spiral curves of the twisting elements; melts are overturned to realize radial mixing, so that the mixing and homogenizing effects of the melts are improved; the melts in the static mixer are mixed through own flowing energy, so that the shearing effect is low, and metal pigment powder is prevented from being further shorn and damaged.