In this work, S-doped Co3O4 (S-Co3O4) and Co3O4 are synthesized by the simple chemical method and their supercapacitive performances are mainly investigated. It is found that S doping increases oxygen defect and conductivity. At 0.2 A g−1, S-Co3O4 electrode has a specific capacitance (155.4 F g−1), which is ~8.8 folds as high as that of Co3O4 (17.6 F g−1). The improved capacitance of S-Co3O4 is mainly due to its larger electrochemical active surface, electric conductivity and more oxygen vacancies: the Brunauer-Emmett-Teller (BET) surface area of S-Co3O4 (15.5 m2 g−1) is 10.6 times higher than Co3O4 (1.3 m2 g−1). Meanwhile, the electron paramagnetic resonance (EPR) signal of S-Co3O4 is 2 times higher than that of Co3O4, indicating S-Co3O4 has more oxygen vacancies than Co3O4. Additionally, the density functional theory calculation shows that the adsorption energy (Ead) of OH− on OV-S-Co3O4 (with oxygen vacancy) (−6 eV) is 3.5, 0.1 and 7.1 times higher than that on OV-Co3O4 (−1.32 eV), S-Co3O4 (−5.4 eV) and Co3O4 (−0.67 eV), which indicates that OH− is easier to adsorb on OV-S-Co3O4 thermodynamically. Oxygen vacancy can serve as the active site to facilitate the adsorption of OH− and facilitate charge transfer, thus accelerating Faradaic reaction kinetics. Furthermore, an flexible asymmetric micro-supercapacitor (AMC) is fabricated with S-Co3O4@carbon fiber positive electrode and activated carbon@carbon fiber negative electrode. The AMC can deliver an energy density of 0.157 W·h·cm−3 at a power density of 10.87 W·cm−3. After 750 cycles, 73% of discharge capacitance is still remained. In addition, the AMC can drive a light emitting diode (3 mm diameter, red) to work. The AMC is flexible that is handy to be embedded in other power supply apparatuses.