Copper and its alloys are used widely in marine environments, and anisotropic corrosion influences the corrosion kinetics of copper. Corrosion of copper in an electrolyte containing ${\mathrm{Cl}}^{-}$ is described as a dissolution–deposition process, which is a prolonged process. Therefore, it is laborious to clarify the corrosion anisotropy in different stages. In this paper, electrochemical impedance spectroscopy (EIS) following elapsed open circuit potential (OCP) test with 0 h (0H), 24 h (24H) and 10 days (10D) was adopted. To exclude interruptions such as grain boundary and neighbor effect, single crystal (SC) Cu$\left(100\right)$ and Cu$\left(111\right)$ were employed. After 10D OCP, cross-sectional slices were cut and picked up by a focused ion beam (FIB). The results showed that the deposited oxide was Cu₂O and Cu$\left(100\right)$/Cu$\left(111\right)$ experienced different corrosion behaviors. In general, Cu$\left(100\right)$ showed more excellent corrosion resistance. Combined with equivalent electrical circuit (EEC) diagrams, the corrosion mechanism of Cu$\left(100\right)$/Cu$\left(111\right)$ in different stages was proposed. In the initial stage, a smaller capacitive loop of Cu$\left(111\right)$ suggested preferential adsorption of ${\mathrm{Cl}}^{-}$ on air-formed oxide film on Cu$\left(111\right)$. Deposited oxide and exposed bare metals also played an important role in corrosion resistance. Rectangle indentations and pyramidal structures formed on Cu$\left(100\right)$/Cu$\left(111\right)$, respectively. Finally, a perfect interface on Cu$\left(100\right)$ explained the tremendous capacitive loop and higher impedance (14,274 Ω·cm²). Moreover, defects in the oxides on Cu$\left(111\right)$ provided channels for the penetration of electrolyte, leading to a lower impedance (9423 Ω·cm²) after 10D corrosion.