The high purity ultrafine chromium oxide was prepared by carbothermal reduction method optimized by response surface method using sodium dichromate separated and extracted from chromium-containing electroplating sludge as precursor.It effectively avoided the disadvantages of environmental pollution caused by a large amount of chromium-containing waste produced in the production process of traditional processes，and achieved the goal of comprehensive utilization of chromium resources and zero pollution emission.The effects of n（C）/n（Na₂Cr₂O₇），reaction time and reaction temperature on RE_Cr（Ⅵ） were investigated.On this basis，the response surface method was used to optimize the selection，and the reactants and reduction products were characterized by thermogravimetric analyzer and X-ray diffractometer.The mechanism of carbothermal reduction was discussed.The results showed that the optimum reduction conditions were n（C）/n（Na₂Cr₂O₇）=4，reaction time of 2 h，reaction temperature of 550 ℃，and the RE_Cr（Ⅵ） reached 99.947%.The significant order from big to small of the influence of various factors on RE_Cr（Ⅵ） was：n（C）/n（Na₂Cr₂O₇），reaction temperature，reaction time.The mechanism of carbothermal reduction was that Na₂Cr₂O₇ was first reduced to Cr₂O₃ and Na₂CO₃ by carbon black during the reduction process，then molten Na₂Cr₂O₇ neutralized Na₂CO₃ to form Na₂CrO₄，and finally Na₂CrO₄ was further reduced to Cr₂O₃ by carbon black.At the same time，the reaction temperature should not be too high，too high reaction temperature would promote the transformation of Cr₂O₃ to NaCrO₂.The purity of the prepared Cr₂O₃ product was more than 99%，and the average particle size was 214.246 nm，which met the first-class quality index of industrial chromium trioxide and met the high-value utilization requirements of materials such as plasma spraying and chrome green pigments.