In the development of low-permeability oil and gas fields with high temperature, high pressure (HTHP), and high acid gas content, the general approach is acid stimulation through an integrated pipe string. In some oil and gas wells, frequent pipe string failures occur during acidification and production. For the purpose of analyzing the corrosion behavior of tubulars in acid environments and the causes of mechanical performance degradation, HTHP circular flow testers were used together with metallurgical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and mechanical performance testing technologies; weight loss experiments and mechanical performance tests were carried out in HTHP kettles for corrosion evaluations and tensile mechanical performance testing on commonly-used P110 tubulars and G3 nickel-base alloy tubulars to evaluate the corrosion degree, corrosion behavior, and mechanical performance change rules of these tubulars during oil and gas production and under different acid conditions. The study results are as follows. (1) During oil and gas production and under different acid conditions, the corrosion rate of nickel-base alloy is much lower than that of carbon steel. (2) With the increase of acid density, the corrosion rates of both nickel-base alloy and carbon steel increase and are greater than 0.076 mm/a which is specified in the NACE Standard RP0775-2005. (3) With the increase of acid density, the number of corrosion pits increases and the corrosion product film becomes thicker on the surface of the nickel-base alloy; and the corrosion product film falls off from the surface of alloy samples in 10% and 20% acids. (4) The mechanical performance of the acidized carbon steel and nickel-base alloy degrades, which becomes more significant as the acid concentration and acid treatment time increase. The degradation of the nickel-base alloy is more significant than that of the carbon steel. The following conclusions are made. (1) Acid treatment should be conducted by separate acidizing string and production string, or the acid time should be properly controlled to avoid pipe string corrosion. (2) Nickel-base alloy tubulars are recommended for exploitation.