The present disclosure relates to a method and an apparatus for representation of a sparse matrix in a neural network. In some embodiments, an exemplary operation unit includes a buffer for storing a representation of a sparse matrix in a neural network, a sparse engine communicatively coupled with the buffer, and a processing array communicatively coupled with the sparse engine. The sparse engine includes circuitry to: read the representation of the sparse matrix from the buffer, the representation comprising a first level bitmap, a second level bitmap, and an element array; decompress the first level bitmap to determine whether a block of the sparse matrix comprises a non-zero element; and in response to the block comprising a non-zero element, decompress the second level bitmap using the element array to obtain the block of the sparse matrix. The processing array includes circuitry to execute the neural network with the sparse matrix.