The upper and lower sides of the conveyor belt are mutually influenced and independent. In general, insufficient parallelism of lower idlers and levelness of rollers will cause deviation on the lower side of conveyor belt. The situation that the lower side runs off and the upper side is normal is basically due to the bad cleaning device, the lower roller is stuck with materials, the counterweight rollers are not parallel, or the counterweight support is skewed, and the lower rollers are not parallel to each other. The specific situation should be adjusted according to the actual situation. Generally speaking, the underside deviation can be corrected by improving the working condition of the cleaning device, removing the roller and the materials stuck on the roller, adjusting the underside flat roller, the underside V-shaped roller, or installing the underside aligning roller.