Considering three twolevel atoms initially in the GHZ state, two atoms of the three atoms are put into initially empty cavity and made resonant interaction. The twoatom entanglement properties inside cavities are investigated by means of the quantum theory and numerical calculations. Through comparing the results if a rotation operation and direct selective measurement is performed or not, the influences of a rotation operation and stateselective measurement of the atom outside the cavity on the twoatom entanglement evolution inside cavities are discussed. The results obtained using the numerical method show that the twoatom entanglement properties inside cavities is controlled by manipulating the atom outside the cavity, and it can be strengthened by seleting suitable rotation angle.