A data compression method and a data decompression method are provided. The method includes pruning an original data including a plurality of weight parameters, identifying at least one first weight parameter of which at least one first value is not changed by the pruning, among multiple weight parameters included in the pruned original data, and obtaining a first index data including location information of the at least one first weight parameter of which the at least one first value is not changed, identifying at least one second weight parameter of which at least one second value is changed by the pruning, among the multiple weight parameters included in the pruned original data, and substituting the at least one second weight parameter of which the at least one second value is changed with a don't care parameter.