The effects of optical field coherence parameter, modular photon number, Kerr medium coefficient and detuning on the entanglement evolution of cascade three-level atom in Kerr medium are studied based on quantum theory and numerical calculation. The results show that the entanglement between atoms is enhanced in stronger optical field and the entanglement become steady by increasing the modular photon number. Kerr effect is remarkable in more photon number. With invariable Kerr medium, the increase of detuning will strengthen the entanglement strength, but this effect primarily incarnates on initial time of interacting.