A new hydrometallurgical process based on the methanesulfonic acid system was proposed to extract the bismuth efficiently from by-products of lead smelting. The bismuth extraction process included electrorefining, oxidation leaching, and electrodeposition. The optimum conditions of the bismuth extraction process were determined by a single-factor test. The bismuth plate with a purity of 99.8% was obtained under the optimum conditions. Cyclic voltammetry and linear sweep voltammetry were applied to investigating the cathode reaction mechanism of electrorefining. The results show that lead deposition, bismuth deposition, and hydrogen evolution occur at the cathode, and the reactions of metals deposition are irreversible and diffusion-controlled. In addition, decreasing the temperature and acidity can improve the purity of the cathodic product (lead powder) in the electrorefining process.