Disclosed is a coil width control method including: a step in which a control unit generates a prediction model for predicting the width shrinkage of a coil, which occurs in the heat-treatment process and post-treatment process of a cold-rolled steel sheet production process, on the basis of historical operating results; a step in which the control unit receives the input width of the coil entering the heat-treatment process; and a step in which the control unit predicts the output width of the coil after the post-treatment process on the basis of the received input width and the conditions of the cold-rolled steel sheet production process, and controls in-furnace temperature and in-furnace tension of the heat-treatment process and elongation of the post-treatment process.