Abstract: By discussing the fabric image and the precision of the scanner in the article,the scanner is used to get high resolution fabric image by scanning in the vertical direction.A specific image size is put forward to analyze the fabric image. The skew of the complete fabric image has been correctly rectified by locating the yarn clearances.The brightness information and the projection curve of the reflect image from the fabric surface are used to confirm the position of the yarn clearances in the processed image.The accurate average distance of the yarn clearance is acquired by checking the distance of the yarn clearances in turn,and then the density of the fabric is calculated from the distance.High reliability of the technique is proved by experiments with a relative error of 0.07%.