Abstract: Corn stalk fibers(CSF)pretreated by different preservatives, and high density polyethylene(HDPE)plastic were mixed and melt-compounded with other additives using a twin-screw extruder, and then molded to produce CSF/HDPE composites. The effects of preservative type and concentration, and CSF loading amount on the mechanical properties of composites were examined using the scanning electron microscope(SEM)and Fourier transform infrared(FTIR). Experiment results indicated that, as the alkaline copper quaternary(ACQ)concentration in the preservative increased, the mechanical properties of the composites decreased. The optimum mechanical property of CSF/HDPE composites was obtained at a CSF content of 50% and ACQ concentration of 1%. When treated with zinc borate(ZB), the tensile strength of the composite increased with the increasing ZB concentration, but the flexural strength, flexural modulus and impact strength firstly increased and then decreased accordingly. In this case, the optimum mechanical property of CSF/HDPE composites was obtained at a CSF content of 50% and ZB concentration of 2%.