Abstract: A negative cluster ion implantation system with “Charge-up free” characteristic was established by installing a sample holder and an electrostatic scanner on the injector of the GIC4117 tandem accelerator. The carbon and cluster carbon negative ion implantation was used for surface modification study of cell biocompatibility of silicon rubber (SR). The measure of water contact angle shows, with an increase in dose up to 3×10¹⁵cm^-2, the water contact angle decreases from about 108.7° to 103.1° and the surface hydrophilicity is promoted. The XPS results indicate, with an increase in dose, the surface composition of carbon atoms decreases while oxygen and nitrogen atoms fraction increases. Based on above results, the mechanism of negative ion implantation cell biocompatibility modification of SR was discussed. Finally, cells were cultured on the sample, and the result shows that negative ion implantation is a convenient and effective method to improve cell biocompatibility of SR.