High-purity scandium oxide is the principal raw material of high-purity scandium metal and aluminum scandium alloy targets for electronic materials. The performance of electronic materials will be significantly impacted by the presence of trace amounts of radionuclides due to the increase in free electrons. However, about 10 ppm of Th and 0.5–20 ppm of U are typically present in commercially available high-purity scandium oxide, which it is highly necessary to remove. It is currently challenging to detect trace impurities in high-purity scandium oxide, and the detection range of trace thorium and uranium is relatively high. Therefore, it is crucial to develop a technique that can accurately detect trace Th and U in high concentrations of scandium solution in the research on high-purity scandium oxide quality detection and the removal of trace impurities. This paper adopted some advantageous initiatives to develop a method for the inductively coupled plasma optical emission spectrometry (ICP-OES) determination of Th and U in high-concentration scandium solutions, such as spectral line selection, matrix influence analysis, and spiked recovery. The reliability of the method was verified. The relative standard deviations (RSD) of Th is less than 0.4%, and the RSD of U is less than 3%, indicating that this method has good stability and high precision. This method can be used for the accurate determination of trace Th and U in high Sc matrix samples, which provides an effective technical support for the preparation of high purity scandium oxide, and supports the production of high-purity scandium oxide.