Abstract: The literature provides references for the accurate determination of silicon content in soil and sediment by inductively coupled plasma-optical emission spectrometry (ICP-OES). Sample decomposition methods often use acid dissolution or melting methods. Silicon reacts with hydrofluoric acid in concentrated acid solution to form volatile silicon tetrafluoride, which is lost due to heating. The melting method can process soil and sediment samples, but it introduces a large amount of salt, a significant matrix effect and high detection limit. This article describes a method for determining silicon content in soil and sediment using ultrasonic sealed acid dissolution and ICP-OES. After the sample was dissolved in dilute aqua regia, hydrofluoric acid, and hydrogen peroxide in an ultrasonic apparatus and diluted to a constant volume, the sample was measured using ICP-OES equipped with a hydrofluoric acid resistant injection system. During ICP-OES testing, 251.611nm was selected as the analytical spectral line for silicon. The correlation coefficient of the standard curve in the range of 5mg/L to 50mg/L was greater than 0.99997, and the detection limit of the method was 0.0395mg/g. This method was used to test different types of soil and sediment standard substances, with relative standard deviations (RSD) ranging from 0.26% to 0.54% and relative errors ranging from −0.28%−0.23%. The actual sample testing RSD range from 0.52% to 0.77%. Verified by national standard substances GBW07401a, GBW07405a, GBW07377, and GBW07379, the measured values of silicon element were consistent with the standard values. At the same time, X-ray fluorescence spectroscopy was used to determine the silicon content in these four national standard substances, and the results were consistent.