A digital control method is to accurately calculate the real-time addition amount of each dye in the solution replenishment system in the whole dyeing process based on the initial dyeing rate of each dye, and replenish the dye solution according to the real-time addition amount. A digital control system includes an automatic calculation K.sub.0,n value unit, a central processing unit and a replenishment pump. The automatic calculation K.sub.0,n value unit is composed of a dye solution concentration detection instrument, a sensor I and a BP neural network model. The BP neural network model is a BP neural network trained by a dye database. The automatic calculation K.sub.0,n value unit transmits the K.sub.0,n value to the central processing unit, calculates the replenishment amount through the central processing unit, and controls the replenishment pump to replenish the solution.