Abstract: The switching noise accompanying in traditional Class-D power amplifier operation limits its wide application in underwater equipment due to its bad impacts on signal reception, communication control and signal transmission. In view of this phenomenon, this paper first explains the principle of reducing switching noise of Class-D power amplifier by using Σ-Δ modulation, and then analyzes and compares the principles of Class-D power amplifier modulated by traditional PWM and Σ-Δ modes with Simulink software. The simulation results show that the traditional Class-D power amplifier generates high energy switching noise at the switching frequency, and the Σ-Δ modulated Class-D power amplifier makes the switching noise energy dispersing in a certain bandwidth, so that the peak energy of switching noise is lower than that of the traditional PWM modulation mode.