High level radioactive waste (HLW) is an extremely dangerous by-product of the global nuclear industry. Due to its intensely radioactive nature and ultra long half-life, HLW has to be safely managed and disposed for thousands of years, isolated from the biosphere. Deep geological repository (DGR) is considered to be the most feasible option worldwide because of its operability, stability, durability, environmental protection and so on. Basically, DGR relies on a multibarrier system and it consists of metallic canisters, backfill materials and a stable geologic formation. Since radionuclides could be moved into the biosphere by action of groundwater, both the geologic formation and backfill materials have to be of very low hydraulic permeability and metal canisters have to be corrosion resistant and prevent contact between the groundwater and the radioactive waste for as long as possible. Low carbon steel has been selected and studied as a candidate canister material in many countries because its long industrial experience, high-strength, low cost and it is less prone to localized corrosion than materials that passivity, but its larger corrosion rate may also set an insuperable barrier for the practical application. Recently, our studies revealed that NiCu low alloy steel is a more promising candidate for the canister material compared with the popular one, low carbon steel, since the former performs a more acceptable corrosion rate without increasing much cost and has better resistance to localized corrosion in environments with high concentration of Cl^-. In this work, effects of SO₄^2-, another ubiquitous species in deep groundwater, on the corrosion behavior of NiCu low alloy steel during immersion in simulated deep groundwater environments were investigated by in situ electrochemical measurements and surface analysis techniques. Results show that the addition of SO₄^2- can promote the substrate dissolution during the initial stage of immersion. In the later stage, SO₄^2- weakens the protectiveness of formed films and consequently, active dissolution prevails on the electrode surface rather than the prepassivation. Concentrated SO₄^2- and HCO₃^- can both promote the formation of Fe₆(OH)₁₂CO₃. The main components of corrosion products are a-FeOOH, Fe₃O₄ and Fe₆(OH)₁₂CO₃, and uniform corrosion is observed.