By using the reduced density matrix operator it was studied the dynamics of a three level atom interacting with the coherent field when the cavity is supposed to be filled with a Kerrlike medium. The property of the evolution of the photonnumber probability distribution is given and the effect of the fieldmedium coupling is discussed. The results indicate that the initial intensity of the field is favourable to the fieldmedium coupling.The stronger the nonlinear fieldmedium coupling is, the more stable the evolution of the photon-number probability distribution which tend to Poisson distribution will be. Some quantum features of the field will tend to be weak and the macroscopic property of the field will tend to be stable while the nonlinear medium interacts with the field.