In view of the environmental pollution caused by the discharge of acidic chromium-containing wastewater, nano-FeS was prepared by ultrasonic assisted method for the treatment of this kind of wastewater. The optimum preparation conditions of nano-FeS were determined by orthogonal test, and the effect of reaction time, pH and initial concentration of Cr(Ⅵ) on the treatment of acidic chromium-containing wastewater by nano-FeS was discussed. The results show that the optimum preparation conditions for the preparation of nano-FeS by ultrasonic assisted method are as follows: ultrasonic frequency 40 kHz, ultrasonic treatment time 10 min, preparation reaction temperature 15 ℃. Under these conditions, the removal rate of Cr(Ⅵ) and total chromium is 81.03% and 63.40%, respectively. When the reaction time reaches 50 min, the treatment effect of nano-FeS on acidic chromium-containing wastewater tends to stabilize. Acidic conditions can facilitate the removal of Cr(Ⅵ) and total chromium by nano-FeS, as the initial concentration of Cr(Ⅵ) increases, the unit removal rate of Cr(Ⅵ) and total chromium by nano-FeS gradually increases. When the initial concentration of Cr(Ⅵ) is 300 mg/L, the unit removal rate of Cr(Ⅵ) and total chromium can reach 486.65 mg/g and 383.55 mg/g. It is found that the nano-FeS prepared by ultrasonic can effectively remove chromium ions from wastewater, which provides some theoretical guidance for practical engineering applications in the future.