Natural fiber, bamboo fiber and PS were used as raw materials to prepare the fiber reinforced composites with certain coupling agents, lubrication agents and plasticizer. The results show that: the mechanical performances of the composites increase with concentration of both fiber and coupling agent, with the optimum value of 25wt% natural fiber and 1.5wt% coupling agent KH550, where the tensile strength, bending strength and elongation rate at break reach 30.2MPa, 86MPa, 8.74% respectively, but the notched impact strength decreases; there exists little deviation on mechanical properties between natural wood fiber and bamboo fiber filled polymer composites.