Abstract: The effects of ultraviolet light intensity on the structure and properties of HDPE were studied. Some oxygen containing groups such as C—O, C O and C ( O) O were introduced onto the HDPE chains by ultraviolet irradiation in air without adding any additives. These groups content and gel contents in the irradiated HDPE increase with the irradiation light intensity under the same irradiation time and environmental temperature. Under the ultraviolet light intensity, the crystal style and cell parameter of irradiated HDPE remain unchanged; the melting temperature and water contact angle of HDPE decrease, while the degree of crystallinity increases, and their variation amplitude increases with the ultraviolet light intensity. Compared with those of HDPE/PVA composites, the mechanical properties of HDPE/PVA composites compatibilized with irradiated HDPE increased. The compatibilization of HDPE irradiated at high ultraviolet light intensity in HDPE/PVA composites is better than that at low ultraviolet light intensity.