The invention relates to the technical field of animal husbandry equipment, and particularly relates to an auto-metering feeding trough, a residual feed metering system and a metering method. The liner of the auto-metering feeding trough is sleeved in a shell, and the liner is internally provided with a plurality of detection height lines respectively in the height direction. The plurality of detection height lines are used to vertically divide the total capacity of the liner into a plurality of parts. The infrared detection components on the various detection height lines is used to respectively detect the residual feed in each part, in order to calculate the volume or capacity of all the residual feed in the liner of the metering feeding trough. Therefore, the metering unit of the residual feed data fed by the feeding trough corresponds to the metering unit of the feeding system, and the calculation may be simplified, in order to avoid the problem that there is often non-intuitive data comparison in data interaction between systems, and the problem that a plurality of conversions cause magnification of an error, which greatly improves the metering accuracy, and ensures provisionof more intuitive and accurate data results.