With the same routing algorithm and network coding scheme, the complexity of network coding (NC) increases with the network scale. In this paper, a network coding scheme based on key nodes is proposed, which is that only the subnet consists of important nodes adopts NC. Using this scheme, the scale of the network that performs NC is reduced, and the complexity of NC is decreased. In wireless network, choosing the steady-going existing nodes as key nodes can increase the stability of network structure. For Some especial network which can not adopt linear NC, part nodes can be chosen as key nodes to perform NC. For super large network, the backbone nodes can be chosen as key nodes. =