In this paper,we propose a physical scheme to realize quantum SWAP gate by using a large-detuned single-mode cavity field and two identical Rydberg atoms.It is shown that the scheme can also be used to create multi-atom cluster state.During the interaction between atom and cavity,the cavity is only virtually excited and thus the scheme is insensitive to the cavity field states and cavity decay.With the help of our scheme it is very simple to prepare the N-atom cluster state with perfect fidelity and probability.The practical feasibility of this method is also discussed.