The method comprises the following steps: acquiring a sparse matrix corresponding to an equation group describing a transmission network state or a device operation state in an iterative solution process; and obtaining a sparse matrix corresponding to the equation group in an iterative solution process. The method comprises: obtaining a sparse matrix corresponding to the equation group; a low triangular matrix being obtained by carrying out LU decomposition on that sparse matrix, and layering the lower triangular matrix by a lazy layering algorithm: For each node i in the lower triangular matrix, if the node i has no child nodes, setting the layer number ei of the node i to the maximum value, and setting the layer number of the parent node of the node i as follows: for each parent node k of the node i, setting the smaller one of the layer number of ek and ei-1 of the k as the layer number of node k; Repeating the above steps to recursively set the layer number of the parent node of node k; adjusting the number of nodes in the lower triangular matrix, putting the nodes into each layer evenly, and getting the matrix value by the previous generation solution.