Abstract: With the help of the dynamic fiber thermo_mechanical analysis,the force and elongation analysis,friction factor analysis,volume resistance analysis and scanning electron microscopy,the influence of binary oil on the properties of PET staple fiber is studied.When the fiber surface is moisturized rapidly by oil solution,the oil also penetrated into the pores between fibers,which results in the change of fiber friction factor,movement of the molecular chain of non_crystalline region,and deformation of fiber.The surface properties of fiber mainly depend on oil pick up (OPU) and environment conditions.The OPU of PET staple fiber should be controlled in the range of 0.15%～0.25%. When the humidity is constant,the smoothness and cohesiveness of the fiber increase with the rising temperature;increasing the humidity improves the antistatic property of the fiber but decreases its smoothness and cohesiveness.