The composite materials, carbon nanofibers-based cobalt oxide and Ag (CoxO-Ag/CNFs) were fabricated through a facile electrospinning method followed by calcination. They were Co2+-Ag/CNFs, Co2+@Co3+-Ag/CNFs. And the Co2+@Co3+-Ag/CNFs sample was obtained through transform Co2+-Co3+ partially by the catalytic oxidation performance of silver, instead of the traditional high-temperature calcination process. Meanwhile, the high conductive of Ag can promote the transportation of electrons and ions between the electrode and electrolyte. The flexible composite materials as free-standing and additive-free film electrodes for supercapacitors. In virtue of the presence of Ag, the composite materials have better conductivity and supercapacitor performance than Co/CNFs-based electrode. Interestingly, the sample of Co2+-Ag/CNFs has a higher capacitors than Co2+@Co3+-Ag/CNFs sample, that indicates the supercapacitor performance has an important relationship with the valence state of cobalt.