Electromagnetic composite rheological polishing (EMRP) is a new ultra-precision machining technology that combines electro-rheological polishing (ERP) and magneto-rheological polishing (MRP). The key technology of the polishing method is the preparation of electromagnetic composite rheological fluid (EMRF) with both electro- and magneto-rheological properties, especially the preparation of composite particles with electro- and magneto-rheological effects. In this study, the EMRF was prepared by using electromagnetic two-phase particles with abrasive characteristics. The electromagnetic two-phase composite particles are synthesized in two steps: the coupling method and sol-gel method. The two-step method successfully prepared the electromagnetic two-phase composite particles with nano-diamond particles embedded randomly on the surface. The electro-rheological shear stress of EMRF can reach 160.7 Pa when the test parameter voltage is 2.5 kV, and magneto-rheological shear stress of EMRF can reach 4076 Pa when the electromagnet excitation current is 3 A. When a fused silica glass is polished under a single magnetic field, the material removal depth reaches a maximum of 2.7 μm at a radius of 13.5 mm. Under the action of the electromagnetic compound field, the removal profile of the work-piece is smoother, and the material removal depth reaches the maximum value of 2.1 μm at a radius of 10.5 mm. This proves that the stiffness distribution of the polishing pad under the electromagnetic composite field is more dispersed than that under a single field. Therefore, the distribution of electromagnetic two-phase composite particles can be controlled by applying an electromagnetic composite field, which provides a good foundation for the abrasive control technology of EMRP.