A convolutional neural network (CNN) method includes determining a temporary buffer layer, which is located between a first layer and a final layer of a CNN system; performing convolutional operations from the first layer to the determined temporary buffer layer of the CNN system in a first stage to generate a feature map line according to partial input data of layers before the temporary buffer layer; and performing convolutional operations from the temporary buffer layer to the final layer of the CNN system in a second stage to generate a feature map.