1. A channel assignment method for a wireless network comprising: a) receiving or collecting node information including available channel information of individual nodes in a wireless network; b) calculating a multi-connection relationship of connection links among the individual nodes using the collected node information; c) calculating a channel conflict relationship caused by interference of the connection links among the individual nodes according to the calculated multi-connection relationship; d) assigning a channel to the connection links among the individual nodes by referring to the calculated channel conflict relationship; and e) transmitting the channel assigned to each link to the individual nodes, wherein the channel conflict relationship calculating step c) includes: c1) calculating all links, each of which includes interference for each node; and c2) generating a multi-channel conflict graph for a connection of the individual nodes by referring to the calculated links, and wherein the channel assigning step d) includes: d1) determining a preferable channel from among the available channels for each node, and extracting a preferable channel list from the available channels for each node; d2) extracting a specific node capable of adapting each of all the channels as a common preferable channel, and generating a sub-graph including only a node extracted from the multi-channel conflict graph; d3) assigning priority for each sub-graph; and d4) assigning a channel to the individual nodes contained in the sub-graph according to the assigned priority, deleting the channel-assigned node from other sub-graphs, and assigning the channel to connection links among the nodes.