A novel scheme for realizing a two-qubit quantum SWAP gate in ion-trap systems is proposed. Two three-level ions are considered which are confined in a linear trap interacting with two different frequency laser pulse in the case of resonance. According to the experimental methods and results of Haffner and Riebe, one Zeeman level of the S1/2 ground state of 40Ca+ ion can act as one ground state, while two Zeeman levels of the metastable D5/2 state as the excited states. With choosing appropriate parameters such as v=1.2 MHz, Ω=0.1v and η=0.1, the total time required to complete the procedure is T≈1.3×10ˉ3s, much shorter than the lifetime Ti≈1.16s of the metastable D5/2 state, and in this scheme decoherence is negligible. Thus this scheme may be realized with presently available ion-trap techniques.