A self-cleaning plasticizing venting and extruding apparatus by co-rotating non-twin multi-screws and a method thereof are provided, said apparatus comprises a screw mechanism, barrel, feeding port, venting port, discharging port, and driving mechanism. Said screw mechanism comprises non-uniform central screw and lateral screws, the axis of the central screw coincides with the barrel, and the lateral screws are provided on both sides of the central screw and engaged with the central screw; the contour lines of the threads of said central screw and said lateral screws are tangent to the inner wall of the barrel; and said driving mechanism is connected to the central screw and lateral screws. Each screw-uses an asymmetrical flow channel shape, so the flow space is asymmetric, and the compounding intensity and effectiveness enhanced. The dispersion and mixing effects are excellent, generating a self-cleaning effect. The system is suitable for high yield nano-material processing.