Abstract: The layer structure and the microstructure of PP hollow fiber membrance were observed by SEM and TEM,and the main structure feature of microstructure of PP hollow fiber membrane used in MO was obtained.The features of PP hollow fiber membrane are that the hollow fiber membrane is nonsymmetrical and the section of the hollow membrance include two layers (cortical layer and bolster layer).The cortical layer has many holes and the bolster layer is sponge structure.The surface layer with opening surface is composed of many irregular microporous.The microporous' arrangement is directional. And they array along with the axis of the fiber.The whole distributing of the porous is even and has high percentage.This structure feature assures that function of MO could be attained successfully.And it can avoid the penetration of the plasma.