A novel silicon oil-based magnetorheological fluids were prepared with carbonyl iron powder as magnetic particles，SiO2 as thixotropic agents,and stearic acid,lauric acid,dimer acid,polyacrylic acid as the surfactants separatedly.The effect of surfactants on tribological properties of magnetorheological fluids was investigated by MMW-1P-utility tribometer,and the worn surface was observed by SEM to analyze the friction mechanism of silicon oil-based magnetorheological fluids.The results indicate that the carboxylic acid-based surfactants can enhance the viscosity of magnetorheological fluids and improve the tribological properties,however the wear mechanism of magnetorheological fluids is still the typical three body abrasive wear.Stearic acid and lauric acid are outstanding in tribological properties for the five kinds of surfactants.