Abstract: The effect of ultraviolet irradiation at different temperatures of environments in air on the structure and properties of high density polyethylene (HDPE) and the compatibilization effect of HDPE functionalized by ultraviolet irradiation in HDPE/polyvinyl alcohol (PVA)-fiber blend systems are studied through FTIR, surface contact angle measurement with water and mechanical properties test. The results show that —C(C=O)CH₃、—CH₂C(=O)CH₂—、—C(=O)O— oxygen-containing groups are introduced onto HDPE molecular chain during ultraviolet irradiation in air. The rate of HDPE functionalization is increased with the temperature of environments. After ultraviolet irradiating, the Young's modulus and tensile yield strength of HDPE are increased; its elongation at break and notched Izod impact strength are decreased. The proper functionalized HDPE behaves as a compatibilizer in HDPE/PVA-fiber blend; by adding 5 wt% functionalized HDPE (irradiation light intensity is 78 W/m² and irradiation time is 24 hours) into the HDPE/PVA-fiber (88/12 wt%), the tensile yield strength and notched Izod impact strength of the blend are increased from 28.3 MPa (HDPE/PVA-fiber: 88/12 wt%) to 30.6 MPa and 130 J/m to 163 J/m respectively.