Abstract: Four kinds of poplar wood fibers (PWF, 125-180 μm, 180-425 μm, 425-850 μm and 850-2 000 μm)/high-density polyethylene (HDPE) composites were prepared by means of hot-compression molding. The flexural property test, impact property test, dynamic thermo-mechanical analysis(DMA), 24 h creep-24 h recovery test and 1 000 h long-term creep tests were performed for PWF/HDPE composites. The results show that the excessively large or small PWF size is not positively for improving the flexural property of PWF/HDPE composites. PWF/HDPE composites with fibers of 425-850 μm present the best enhancement effect. The flexural strength and the elastic modulus of 425-850 μm PWF/HDPE composites are 26.71 MPa and 2.73 GPa, respectively. Impact resistance property of PWF/HDPE composites keeps constant, while the PWF size increases from 180 μm to 2 000 μm. Whereas, 125-180 μm PWF/HDPE composites have the lowest impact resistance property. The PWF/HDPE composites with small fibers have the worst anti-creep performance, indicating that it is not suitable for long-term loading. 850-2 000 μm PWF/HDPE composites with long fibers have outstanding long-term anti-creep performance and recovery (78.46%), and its 1 000 h deformation is just 0.809 mm, which compares with the average values of 1 000 h deformation for other PWF/HDPE composites and decreases by 48.00%.