The foreign matters of raw cotton seriously affect the cotton grade and the quality of the final woven product. Detecting and eliminating of the foreign materials from raw cotton is difficult during the spinning operations. Many researchers have applied different techniques to identify various contaminations of raw cotton based on their characteristics of geometry, physics and spectroscopy. These techniques are machine vision at visible light wave, infrared spectroscopy, X-ray micro-tomographic image, and so on. Different kinds of sorter have been developed since the 1950s. For improving the detection accuracy of different foreign matters in complicated condition, the techniques of real-time infrared spectroscopy, multispectral and hyperspectral imaging will be adopted gradually. 