We investigated the entanglement time evolution of two entangled two-level atoms. The two atoms can undergo multiphoton transition when they interact resonantly with a single-mode field in the coherent state. The results show that the two-atom entangled state evolves periodicity. The influence of the two-atom initial state，the dipole-dipole coupling intensity between two atoms，the parameter of the coherent state and the number of the transitional photons on the entanglement degree of two atoms are revealed. When the initial state is a maximum entangled state，the state of the two entangled atoms will forever stay in this maximum entangled state. So this kind of entanglement state can be used for quantum information storage.