To solve the problem of high trash content and poor quality of the output cotton in the cleaning and combing process,a local motion impurity ratio control optimization method is proposed by combining the improved Gaussian mixed model (GMM) and frame difference method.Firstly,the principle of the cleaning machines and the characteristics of the trash is analyzed cotton.Secondly,by extracting the key frames of the video,and combining the improved GMM and the frame difference method,the target is accurately extracted by the "with" operation of the image sequence,and then by designing the GMM classifier to obtain the cotton impurity rate for analysis.Finally,it is compared with the traditional detection algorithm for validation.Experiments show that the improved algorithm is better than the traditional algorithm in terms of effectiveness as well as practicality.At the same time,it can meet industrial high precision and real-time requirements by introducing closed-loop control.