A process of producing a cathode electrocatalyst for metal-air batteries, comprising: providing a carbon source suspension that includes an inorganic carbon source, a metal source solution including a metal source and having a pH value ranging from 6.5 to 10.5, and a nitrogen source solution including a nitrogen source, the metal source being formed from a soluble ionic compound and being selected from the group consisting of a cobalt source, a manganese source, an iron source, a nickel source, a chromium source, and combinations thereof, the nitrogen source being formed from a nitrogen-containing organic compound; subjecting the carbon source suspension and the metal source solution to a low-temperature hydrothermal reaction so as to form a first precursor-containing product that includes a first precursor, the metal source from the metal source solution being doped on a surface of the inorganic carbon source from the carbon source suspension to form the first precursor of the first precursor-containing product, the low-temperature hydrothermal reaction being conducted at a temperature ranging from 70°C to 85°C for at least 20 hours; subjecting the first precursor-containing product and the nitrogen source solution to a high-temperature hydrothermal reaction, so that the nitrogen source from the nitrogen source solution is decomposed to form nitrogen atoms which are further bonded to the metal source on the first precursor to form a second precursor, the high-temperature hydrothermal reaction being conducted at a temperature exactly or substantially of 180°C for at least 12 hours; and subjecting the second precursor to a heating treatment under a protective atmosphere, so that the second precursor undergoes a phase transition, the heating treatment being conducted at a temperature ranging from 200°C to 900°C. providing a carbon source suspension that includes an inorganic carbon source, a metal source solution including a metal source and having a pH value ranging from 6.5 to 10.5, and a nitrogen source solution including a nitrogen source, the metal source being formed from a soluble ionic compound and being selected from the group consisting of a cobalt source, a manganese source, an iron source, a nickel source, a chromium source, and combinations thereof, the nitrogen source being formed from a nitrogen-containing organic compound; subjecting the carbon source suspension and the metal source solution to a low-temperature hydrothermal reaction so as to form a first precursor-containing product that includes a first precursor, the metal source from the metal source solution being doped on a surface of the inorganic carbon source from the carbon source suspension to form the first precursor of the first precursor-containing product, the low-temperature hydrothermal reaction being conducted at a temperature ranging from 70°C to 85°C for at least 20 hours; subjecting the first precursor-containing product and the nitrogen source solution to a high-temperature hydrothermal reaction, so that the nitrogen source from the nitrogen source solution is decomposed to form nitrogen atoms which are further bonded to the metal source on the first precursor to form a second precursor, the high-temperature hydrothermal reaction being conducted at a temperature exactly or substantially of 180°C for at least 12 hours; and subjecting the second precursor to a heating treatment under a protective atmosphere, so that the second precursor undergoes a phase transition, the heating treatment being conducted at a temperature ranging from 200°C to 900°C.