In-situ tensile tests of a chemically corroded single crystal superalloy were conducted on at 980℃ and 1100℃. The phase transformation in the surface areas during tensile processes were analyzed using field emission scanning electron microscopy (FSEM), energy dispersive X-ray spectroscopy (EDS), electron probe X-ray microanalysis (EPMA) and transmission electron microscope (TEM). The reasons for the phase transformation on the surface and its impact on the alloy were studied through combining the observations and dynamic calculations. Eventually, the effects of phase transformation on the alloy were analyzed. Chemical corrosion promotes precipitation of topologically close-packed (TCP) μ-phase and σ-phase on the surface of the alloy during tensile tests at elevated temperatures. The amount and size of the two phases precipitated on the surface at 1100℃ are greater than those at 980℃. The precipitation of TCP phase on the surface of the alloy results in variation of alloying elements distribution beneath the surface. The depth of the element diffusion at 1100℃ is greater than that formed at 980℃. The precipitation of TCP phase prompts the phase transition from γ phase to γ′ phase around the TCP phase.