Based on the Huygens-Fresnel principle and the unified theories of coherence and polarization of partailly coherent beams, the diffraction properties of vector random electromagnetic beam transmitted through the ring aperture has been investigated. It is found that the intensity distribution, the degree of coherence and the degree of polarization of diffracted beams are related to the interception ratio of circular ring and initial coherence. The intensity distribution of vector random electromagnetic beam is chain structure by diffraction, and the chain structure gradually enlarges. If initial coherences of the incident beam in the x direction and y direction are equal, the degrees of coherence and polarization of the diffracted beam are same as intensity of light. On the other hand in the optical axis of the diffracted beams intensity distribution, degrees of the coherence and polarization exist oscillation. Moreover, when the intensity is maximum in optical axis of the diffracted beams, the degrees of coherence and polarization is minimal, and vice versa.