For the determination of trace indium in copper smelting dust, the standard method adopts flame atomic absorption spectroscopy, and the determination range of indium content is 0.020 0%～0.100%, which cannot achieve the determination of indium content below 0.020 0%. To determine indium content below 0.020 0%, reference is made to the national standard “Chemical Analysis Method for Zinc Concentrates”. However, during the testing process, trace amounts of indium need to be extracted with butyl acetate and back extracted with hydrochloric acid solution. The steps are cumbersome, the operation is complex, and the analysis is time-consuming, which cannot be quickly combined with scientific research in mineral processing and metallurgy. This article studies the coupling of spectroscopy with sensitizer acetone (Ac) in the presence of surfactant Triton X-100 (OP) in a hydrochloric acid medium, which suppresses the interference of lead, zinc, copper, bismuth, and other elements and reduces the detection limit of trace indium in copper smelting dust. Mechanism studies have found that under certain conditions, indium ions, acetone, and Triton X-100 form ternary complexes, which synergistically enhance the atomic absorption spectra of indium, improve the intensity of indium atomic absorption spectra, and increase their sensitivity-using multiple linear regression analysis to fit the concentration relationship between absorbance (A) and indium (In), acetone (Ac). The P values of c_In, c_Ac and c_Op in the fitting results are all less than 0.05, indicating that the three significantly impact absorbance. Using multiple linear regression analysis to find the extremum method, the molar ratio of the ternary complex was calculated to be 1∶1∶2. In addition, this article studied the spectral characteristics of indium determined by flame atomic absorption spectroscopy, the additional amount of acetone and Triton X-100, the selection and addition amount of acid types, acetylene flow rate, and the influence of coexisting ions. Comparative experiments were conducted using the extraction method, and mathematical statistics analyzed the results. The conclusion was drawn that this method has good accuracy and precision and can be used for the analysis and detection of trace indium in copper smelting dust; The detection limit of the method was determined using reagent blank, and at a confidence level of 99%, the detection limit of the method was 0.001 0%, which is 20times lower than the industry standard method.