Abstract: High pure magnesium oxide product purity reaches 99.9%. The silicon impurity content is one of the important indicators to evaluate its grade, and it is particularly important to determine it accurately. Routine standard curve methods cannot overcome the matrix effect of magnesium so that domestic counterparts routinely use matrix matching method to overcome such effect, but it is difficult to find magnesium containing miscellaneous elements and higher purity similar to high purity magnesium oxide products. The standard accession method is used as a technical means since its advantage is that it is very suitable for analyzing (super) trace elements in high magnesium matrix concentrations with high accuracy. This study dissolved the samples of hydrochloric acid. Taking the standard addition method as the technical method, inductively coupled plasma emission spectroscopy was used to establish a simple, fast, and accurate assay. The proposed method had a good linear relationship at the analytical spectral line of 251.611 nm, the detection limit of the method was 0.018 3 μg/mL, and the lower limit of determination was 0.061 0 μg/mL. In the actual high-purity magnesium oxide product test, the calibration recovery rate was between 97.86%-103.80%, which was suitable for determining acid-soluble silicon in high-purity magnesium oxide products and provided technical support for the determination of acid-soluble silicon content in magnesium oxide products of salt lake chemical enterprises.