The invention relates to a screw specially used in a blow molding machine, which can use powder resin; the screw is made of the material of 38CrMoAl high-quality alloy steel and consists of a feeding section with helixes of unequal distance and depth and the length of 5 to 7 pitches, a compression section with helixes of equal distance and unequal depth and the length of 8 to 10 pitches and a metering section with helixes of equal distance and depth and the length of 10 to 12 pitches; wherein, the outer diameter of an integral screw edge of the screw is in unequal diameter gradual enlargementtype; the size of the outer diameter of a screw edge of the extreme end of the metering section is larger by 1 to 2mm than that of the outer diameter of the most front end of the feeding section . The purpose of producing high-quality PVC blow molding films by directly using a powder resin mixing material as the raw material can be realized by increasing compression ratio, prolonging plasticizingtime, adjusting the rotational speed of the screw, changing technical parameters of the screw such as the length-diameter ratio of the screw and changing performance indexes. A single-screw extrudingmachine of the screw, which can directly adopt the powder resin mixing material as the raw material, is widely used for producing PVC blow molding fruit-vegetable fresh-keeping films.