The adsorption performance and mechanism of converter steel slag for Ni2+ in aqueous solution were discussed from the aspects of steel slag dosage, adsorption time and acid conditions, and the effect of Cu2+ on the adsorption of Ni2+by steel slag was also discussed. The results show that when 100 mL Ni2+ solution with a concentration of 50 mg·L-1 is treated with 200 mesh (0.074 mm) 0.15 g steel slag at 25 ℃ for 30 min, the adsorption capacity of Ni2+ is 33.290 mg·g-1 (adsorption rate is 99.88%). The adsorption process of Ni2+ by steel slag conforms to the pseudo-second-order kinetic equation and Freundlich isothermal model, and the correlation coefficient R2 is 0.984 and 0.994, respectively. The adsorption of Ni2+ and Cu2+ by steel slag belongs to competitive adsorption, and the adsorption capacity of Cu2+ by steel slag is better than that of Ni2+. When the pH value is very low, the adsorption effect of steel slag on Ni2+ and Cu2+ is poor. The adsorption process of steel slag on Ni2+ is mainly chemical adsorption, accompanied by physical adsorption, and with the decrease of adsorption sites on the steel slag surface, the physical adsorption of steel slag on Ni2+ will gradually weaken. The research may provide some guidance to the treatment of industrial wastewater containing Ni2+ and Cu2+.