The carbon fibers / rubber composite films were fabricated by compression molding method with butyl rubber (IIR) as matrix and carbon fiber as reinforced material. The mechanical properties and electromagnetic shielding effect of the thin films at different conditions were measured by the WDW electronic universal testing machine according the national standard GB13022-91 and the far-field EMC shielding effectiveness test fixture (DN1015 type) respectively. The results show that the good mechanical properties of composite films with mess ratio of IIR and carbon black of 1:6 and vulcanizing time of 1.5h were obtained at the same other condition that the tensile strength reached 534.65MPa, the elongation rate reached 87.26% and the yield point stress up to124.85MPa. Meanwhile, it is also found that the electromagnetic shielding effect of the thin films shows negative growth at low frequency area ranging from 1MHz to 300MHz. Whereas, the shielding effect increases with frequency at 300MHz ~ 1.5GHz, and the SE value is up to -25dB ~-35dB.