Abstract: The relationship between the content of basalt fiber (BF) and the mechanical properties of basalt fiber reinforced wood plastic composites (BF/WPC) was studied. The reinforcement mechanism of the materials was also discussed. The results show that except a little decline of elongation, the tensile strength, impact strength and bending strength of BF/WPC are enhanced and the maximum of them increases about 30%, compared with pure WPC, when the content of BF is between 15%~30%, 15%~25% and 20%~30%, respectively. Therefore, a qualitative hypothesis that the end cross section of BF is the "weak link" is proposed, which could explain the maximum range between the strength index and the mass fraction of fiber.