The entropy properties of the light field of coupled identical Λtype threelevel atoms interacting with vacuum field in cavity filled with Kerr medium were investigated by means of quantum theory.The time evolutions of the entropy of the light field were discussed via the initial state of the system,detuning,coupling coefficient between the atoms,and the Kerr coefficient.Numerical calculation results show that the evolution of the entropy of the light field exhibits periodic oscillation,and its frequency and amplitude are intensively dependent on the initial state of the system.When the detuning the oscillation amplitude decreases with the increases of coupling strength and Kerr coefficient.