A method for sending a cross-connection command, applied to a centralized controller, wherein a network comprises p nodes; the centralized controller is connected to the network by using k access nodes of the p nodes, wherein p≥k≥2, and both k and p are integers such that the centralized controller is connected to the network by using at least two access nodes; and the method comprises: removing, for each of the access nodes, k-1 links between the centralized controller and k-1 access nodes except the access node, to obtain k different single-homed network topologies; generating, based on the k single-homed network topologies, k initial single-homed subtrees, wherein each of the k initial single-homed subtrees is a minimum spanning tree that uses the centralized controller as a root node and is connected to the centralized controller through one access node; (para 80, 52) generating, by using the k initial single-homed subtrees, k balanced single-homed subtrees, wherein the k balanced single-homed subtrees comprise the p nodes, nodes in any two of the balanced single-homed subtrees have no intersection, quantities of nodes in the k balanced single-homed subtrees are balanced; wherein the nodes in any two of the balanced single-homed subtrees have no intersection if a node of the p nodes is in a balanced single-homed subtree, the node does not exist in the remaining k-1 balanced single-homed subtrees; and wherein the quantities of nodes in the k balanced single-homed subtrees are balanced if a difference between the quantities of the nodes in any two of the single-homed subtrees≤k - 1; and concurrently sending cross-connection commands to the nodes in the k balanced single-homed subtrees in a descending order of layer numbers of layers at which nodes in each of the balanced single-homed subtrees are located, wherein each layer contains nodes with same hop count distance from the centralized controller and a layer number of the layer is the hop count distance of the one or more nodes located at the layer; wherein the acquiring k balanced single-homed subtrees comprises: determining p×(k-1) operational nodes in the k initial single-homed subtrees; and removing the p×(k-1) operational nodes, to obtain the k balanced single-homed subtrees; removing, for each of the access nodes, k-1 links between the centralized controller and k-1 access nodes except the access node, to obtain k different single-homed network topologies; generating, based on the k single-homed network topologies, k initial single-homed subtrees, wherein each of the k initial single-homed subtrees is a minimum spanning tree that uses the centralized controller as a root node and is connected to the centralized controller through one access node; (para 80, 52) generating, by using the k initial single-homed subtrees, k balanced single-homed subtrees, wherein the k balanced single-homed subtrees comprise the p nodes, nodes in any two of the balanced single-homed subtrees have no intersection, quantities of nodes in the k balanced single-homed subtrees are balanced; wherein the nodes in any two of the balanced single-homed subtrees have no intersection if a node of the p nodes is in a balanced single-homed subtree, the node does not exist in the remaining k-1 balanced single-homed subtrees; and wherein the quantities of nodes in the k balanced single-homed subtrees are balanced if a difference between the quantities of the nodes in any two of the single-homed subtrees≤k - 1; and concurrently sending cross-connection commands to the nodes in the k balanced single-homed subtrees in a descending order of layer numbers of layers at which nodes in each of the balanced single-homed subtrees are located, wherein each layer contains nodes with same hop count distance from the centralized controller and a layer number of the layer is the hop count distance of the one or more nodes located at the layer; wherein the acquiring k balanced single-homed subtrees comprises: determining p×(k-1) operational nodes in the k initial single-homed subtrees; and removing the p×(k-1) operational nodes, to obtain the k balanced single-homed subtrees; determining p×(k-1) operational nodes in the k initial single-homed subtrees; and removing the p×(k-1) operational nodes, to obtain the k balanced single-homed subtrees;