The effect of absorbed dose irradiated in vacuum and air on the crystallinity of drawn HDPE was studied. Experimental results show that up to 250kGy of absorbed dose when irradiated in vacuum,the crystallinity of drawn HDPE is decreased from about 75% to about 71%,and then the increase of absorbed dose until 1000kGy has no further effect in lowering thecrystallinity; when irradiated in air,an absorbed dose of 1000kGy has noeffect on the crystallinity of drawn HDPE. The effect of temperature of thermal treatment on the crystallinity of unirradiated drawn HDPE was alsoinvestigated. At first,the crystallinity is increased with the increase oftemperature of thermal treatment, at about 120℃,it reaches the maximumvalue, and then it is repidly lowered with the further increase of temperatureof thermal treatment. Based on the existence of a lot of voids and latticedefects inside the drawn HDPE,the above experimental results were explained.