Abstract: There are provided a system and method of optimization of operating a Convolutional Neural Network (CNN), the method including: for each given layer of the CNN, obtaining at least one input feature map, retrieving an index of one or more filters in the given layer; generating one or more output feature maps corresponding to the one or more filters, including: for each given block, querying the index to find a number of selected filters meeting a predetermined criterion related to respective inner products between the selected filters and the given block, applying the selected filters on the given block to obtain a number of output values for a given output position in a number of output feature maps corresponding to the number of selected filters, and filling in the given output position in the rest of output feature maps with a value of zero, thereby reducing the computational cost of operating the CNN.