Single atom catalysts (SAC) have been investigated extensively for CO oxidation, and penta-graphene (PG) as a new allotrope of carbon has been studied due to its excellent physical and chemical properties. In order to explore the mechanism of CO oxidation and develop the application of PG in the field of SAC, series of metals doped PG were examined to catalyze CO oxidation with the aid of first-principles calculations. Fe doped at 3-coordinated carbon site of PG is found favorable with large binding energy of -12.73 eV, more importantly, exhibits high affinity to the CO and O2. Furthermore, CO oxidation via Eley-Rideal (ER) mechanism is prior compare with Langmuir-Hinshelwool (LH) mechanism, the first CO molecule oxidation is the rate-determining step (RDS) with the energy barrier of 0.51 eV, which is comparable with other catalysts. In the case of Fe doped at 4-coordinated carbon site, ER and LH mechanisms are almost the same because of the similar energy barrier (0.60 eV and 0.59 eV). On the basis of reasonable first-principles calculations, the proposed Fe doped PG is believed to be a promising single atom catalyst for CO oxidation, and our results provide deep insights to design new heterogeneous catalysts based on PG.