It is vital to remove cadmium from wastewater because of its potential harm to the natural environment and human health. It was found that sulfate-reducing bacteria (SRB) had a good fixing effect on Cd under a strict anaerobic environment. However, there are few reports on the immobilization effect and mechanism of SRB on Cd in an anoxic environment. This study revealed the effects of initial Cd²⁺ concentration, initial SO₄²⁻ concentration, temperature, pH, and C/N ratio on the immobilization of Cd²⁺ by SRB in aqueous solution under an anoxic environment. The experimental results showed that under the conditions of initial concentration of Cd²⁺ within 0 mg/L~30 mg/L, initial concentration of SO₄²⁻ within 1200 mg/L, temperature within 25 °C~35 °C, pH neutral, and C/N ratio of 20:1, the immobilization rate of Cd²⁺ by SRB is above 90%. The characterization results showed that bioadsorption and chemical precipitation were the main mechanisms of SRB immobilization of Cd²⁺ in an anoxic environment.