Combinational metals of casing or tubing string have been extensively used in deep sour gas wells because of their corrosion resistance and low costs. C110 carbon steel and G3 alloy connected by a thread joint under different stresses represent a typical application of dissimilar metals in such a case. Around the contact part, complex corrosion can occur, including general, galvanic, and stress corrosion. To evaluate such corrosion, simulation experiments were conducted. Three specimens involving (1) a single piece of C110, (2) a galvanic couple of G3 alloy and C110, and (3) an elastic- and plastic-stressed C110 were separately placed in a high-pressure and high-temperature (HPHT) autoclave containing brine water and dissolved H2S, CO2, and elemental sulfur. After corrosion at 120 degrees C and 65 MPa for seven days, the specimens were examined by various methods, including weight loss, potential dynamic polarization, electrochemical impendence spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectrometry (XPS). The experimental results showed that sour corrosion of C110 in the vapor is similar to that in solution. The galvanic effect on C110 corrosion by G3 was not evident based on the measurement of the limited increment of corrosion rate. Slower acceleration for corrosion was also observed for C110 when elastic stress was applied. However, plastic deformation significantly stimulated the corrosion rate of C110. The yield strain was found to change the polarization behavior of the anode and the performance of the corrosion scale. The corrosion mechanism is discussed in detail based on an analysis of the surface morphology, composition, and electrochemical performance of the scale, together with theories of the supercritical state, semiconductors, and mechano-electrochemistry.