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A Co-based coating was prepared on the surface of PCrNi3MoVA steel via plasma transferred arc (PTA). A modified pressure-vented vessel was used to simulate the high-speed airflow environment generated by the propellant combustion in gun bore, and an accelerated erosion was performed on the coating under this experiment. The eroded surface was analyzed using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). The thermal behavior of the coating melting process was analyzed by differential scanning calorimetry (DSC). Results show that the coating mainly contains Co solid solution dendrites, and intergranular eutectic structures formed by Co solid solution and carbide. Coating erosion mainly occurs on the eutectic structure, which is manifested by the melting and peeling off of this structure accompanied by oxidation reactions. The cracking mechanism of the coating mainly comprises low-temperature brittle cracking of hard carbides and stress concentration cracking after low melting eutectic removal under transient high-speed heat airflow scouring. • Coating erosion is manifested by the melting and peeling off of the eutectic structure. • The erosion is accompanied by unsteady oxidation reactions. • Embrittlement cracking occurs on the low-plasticity hard phase under transient temperature shock. • Stress concentration produces cracks after low melting eutectic removal. [ABSTRACT FROM AUTHOR]