Cotton stalk is a by-product of cotton planting process, and a great resource as a raw biomass material for manufacturing value-added composite products. The fine structure and fiber size of the cortex, xylem of the cotton stalk were studied in this paper. In addition, a new method for the processing of cotton stalk filament was developed. Composites consisting of polypropylene (PP) and cotton stalk filament were prepared by hot pressing. The effects of PP content and compressing temperature on the mechanical properties of cotton stalk filament /PP composites were studied. The results show that elevated temperatures, all of the composites are substantially stiffer and stronger than that at lower temperature. PP content improves the intensity and adhesion of composites. Simultaneous optimization of composites properties indicates that the composites with PP content of 40% and the compressing temperature of 195°C would sufficient meet the requirements of the GB/T 4897.1-2003 standard. Bio-renewable materials such as cotton stalk can be used as reinforcing materials for plastic composites.