Abstract: In order to solve the current problems of long time consuming, low extraction efficiency and matrix interference on detection of hexavalent chromium in soild waste, hexavalent chromium in solid waste was determined by ultra trace hexavalent chromium analyzer combined with ultrasonic extraction and post-column derivatization ion chromatography. The solid waste sample(2.0 g) was taken into a 50 mL-colorimetric tube, followed by 40 mL of alkaline extraction reagent including 20 g·L⁻¹ sodium hydroxide and 30 g·L⁻¹ sodium carbonate, 0.4 g of magnesium chloride and 0.5 mL of buffer solution including 68.7 g·L⁻¹ dipotassium hydrogen phosphate and 87.1 g·L⁻¹ potassium dihydrogen phosphate, and the mixture was shaken well, and extracted by ultrasound at a power of 50 W for 45 min. The extract was centrifuged for 10 min, and the supernatant was taken, and made its volume to 50 mL with water. Hexavalent chromium was determined by ion chromatography using a solution containing 0.67% (volume fraction) nitric acid and 1% (volume fraction) ammonia water (pH 8−9) as the eluent for isocratic elution and 1% (volume fraction) sulfuric acid solution containing 0.8 g·L⁻¹ diphenylcarbazide as the derivatizing agent. As shown by the results, linear relationship between the corresponding peak area and mass concentration of hexavalent chromium was kept within 2 000 µg·L⁻¹. The detection limit was 0.3 µg·L⁻¹ (0.008 mg·kg⁻¹), which was better than those of HJ 687—2014 (2 mg·kg⁻¹) and GB/T 15555.4—1995 (0.004 mg·L⁻¹). RSDs(n=6) of the determined values of hexavalent chromium in solid waste standard sample for the precision test was in the range of 2.6%−2.9%, and the relative error was in the range of −3.5%−0.49% for the accuracy test. This method was used to analyze the blank coal spiked samples, and there was no significant difference between the results of this method and HJ 687—2014.