In order to solve the problems of low impurity removal efficiency and high cleaning cost in the process of cleaning after machine harvesting of membrane impurities, a membrane impurity separation method was proposed, which was first turbulent diffusion and then air gravity separation, and a perturbative membrane impurity separation device was designed. Through the theoretical analysis of the process of residual membrane turbulent diffusion and membrane miscellaneous air separation, it was determined that the key factors affecting the separation performance were the inlet air velocity, turbulence angle, diffusion chamber outlet height and conveying speed. Based on the discrete element model of residual film, cotton straw and soil miscellaneous materials, the EDEM-Fluent coupling simulation was used to numerically simulate the separation process of membrane impurities, which revealed the movement law and distribution of membrane miscellaneous materials after crushing in the separation device, and provided a basis for the structural parameters and working parameters of the separation device. Experimental tests with the prototype device, using impurity removal rate and winnowing loss rate as evaluation indices, determined the influence of different factors on performance. Optimal parameters were found to be: a turbulence angle of 48°, inlet air velocity of 5.8m/s, and diffusion chamber outlet height of 178.5mm, achieving an 80.26% impurity removal rate and a 12.35% film leakage rate. These results can meet subsequent resource utilization requirements and offer valuable guidance for advancing winnowing impurity removal technology in mulch film separation.