Objectives: To meet the requirements of high cleaning rate and low loss rate. Methods: A small negative pressure winnowing machine for walnut shell and kernel mixtures was developed. Single factor test and response surface optimization method were used to analyze the working parameters of winnowing machine based on such two separation effect indicators as cleaning rate and loss rate. Results: For 1/2 shell kernel, 1/4 shell kernel, 1/8 shell kernel and 1/16 shell kernel materials, the optimal feeding rates were 4.0， 3.5， 3.0， 2.5 kg/min, the fan frequencies were 40， 35， 30， 30 Hz, the feeding inlet heights were 400， 400， 300， 300 mm, respectively. It was seen from the separation effect of different grades of walnut shell materials that 1/2 and 1/4 shell kernel materials had the best separation effect. Conclusion: Shell and kernel separation can be effectively realized by controlling the working parameters of winnowing machine. It is difficult to separate 1/8 and 1/16 shell kernel materials for the overlapping range of suspension speed of shell and kernel materials.