We propose a theoretical scheme for secure quantum key distribution network following the ideas in quantum dense coding. In this scheme, the server of the network provides the service for preparing and measuring the Bell states, and the users encodes the states with local unitary operations. For preventing the server from eavesdropping, we design a decoy when the particle is transmitted between the users. It has high capacity as one particle carries two bits of information and its efficiency for qubits approaches 100%. Moreover, it is not necessary for the users to store the quantum states, which makes this scheme more convenient for application than others. ; Comment: 5 pages, 2 figures. The decoy-photon technique is presented in a clear way for preventing a potentially dishonest server on a network from eavesdropping quantum communication freely. This technique may be useful in quantum secret sharing (of classical information or quantum information), controlled teleportation, and so on