In this paper, we studied the evolution of a system of two atoms of different energy levels interacting with a single-mode optical field, with one atom in the ground state and the other in the excited state. Entanglement between atoms was studied using partial transposition of negative eigenvalues and the effects of the dyadic interaction and the photon number on the evolution of the entanglement between the two atoms were discussed separately. The results show that increasing the coupling interactions and decreasing the photon number can lead to increased interatomic entanglement, and that increasing both coupling interactions and photon number can lead to shorter interatomic evolution periods. This study will help to find ways to enhance interatomic entanglement.