Magnetorheological elastomers are a new kind of MR materials, which consist of magnetizable particles and elastomers. Because of the controllable orheological properties, the materials show a widely prospect in engineering application. In this paper, the magnetic-induced modulus under shear-compression mode was studied. Based on the modulus, the relative MR effect and its influence factor were systematically analyzed. The results show that the relative MR effect will increase with the increasing volume fraction of magnetizable particles, the exterior magnetic field strength and compression strain, and decrease with the increasing shear strain and modulus of matrix. For the study of the relative MR effect, it will give useful advices for the design of MR materials and MR devices.