Present methods using spectral reflected imaging for detection of lint trash suf fer from some fundamental limitation because the trash almost has the same refl ected characteristic as the lint. To effectively detect the trash in lint, a met hod using transmitted imaging technique was proposed and the experimental pheno menon was analyzed in detail. The transmitted imaging model was constructed bas ed on analyzing the trash and lint absorption characteristics. And the impacts o n imaging target by the type and energy of light source as well as thickness an d velocity of lint movement were also discussed. After analyzing the transmitted photo propagation characteristic, a method of capturing non-diffuse photo using high-speed CCD and statistic filtering processing was developed for enhancement of the imaging target. Furthermore, the relation between the exposure time of high-speed CCD and the target distinctness was determined. The result indicated that the method is effective to acquire a distinct target image using the transmitted imaging detection and imaging target enhancement. And the image is consistent with the actual target. This method not only can provide an effective way to detect the white and colorless trash in cotton, but also can be applied to other imaging system such as the infrared and other band spectral imaging. It is believed that this weak target transmitted imaging system is an effective way to detect wcak target.