Abstract: The plastic mulch culture of cotton in Xinjiang results in the mixing of plastic residual into cotton in the mechanical harvesting process. What’s more, the presence of film remnant is one of the key factors reducing the quality level of mechanical harvested cotton. To clean the film remnant more efficiently, one kind of mesh roller-type cotton and film remnant separator was designed. The motion equations of separating objects in separation device were constituted, and the DPM model was used to analyze the separation principle of unginned cotton and film remnant. As a result, unginned cotton trajectories based on mathematical model and CFD simulation analysis explained the remnant membrane separation process. The effect of flow speed at the entrance of the separation equipment was tested, and the results showed that the best cotton inlet velocity was 4.5 m/s with acceptable separation effect.