The time evolution of atom’s occupation in a double Jaynes-Cummings model, where two atoms are in mixed state, was investigated by full quantum theory and numerical method, and the influences of atomic initial state and mean photon number in cavity on atom’s occupancy are discussed. The results show when the two cavities have the same photon number, evolution of atom’s occupation is only related to the purity of atomic initial state and field intensity, but not influenced by initial entanglement. If the mean photon number in cavities is not equal, the evolution of atom’s occupation is not only related to the purity and field intensity, but also strongly influenced by the initial entanglement.