A scheme that Λ-type three-level atoms are used to entangle movable mirror and cavity field in a Fabry-Perot cavity is proposed. The mechanism that the stable entanglement of optomechanical system can be generated through radiation pressure is presented. It is shown that the larger stationary entanglement can be obtained with the existence of atomic mediums. The criterion of Simon is employed in the proposed scheme to determine the entanglement, and the logarithmic negativity is used to quantify the stable macroscopic entanglement of the system. It is found that the larger entanglement corresponds to the larger coupling between the cavity and the atoms. With the help of atoms, the maximum entanglement of the system increases from 0.5 to 2.05. And such macroscopic entanglement still exists even for bad cavity limits.