Abstract: In this paper, the amplitude spatial distribution characteristics of normal modes in a horizontally layered environment are investigated. A mathematical model is established using the boundary conditions of the layers to analyze the amplitude distribution patterns of normal modes in different layers and discuss the influence of environmental parameters on the vertical amplitude distribution of normal modes. Simulation results from typical layered environments, such as sedimentary layers with constant density and sound velocity, and sedimentary layers with a positive gradient of density and sound velocity, show that the amplitude of normal modes is closely related to the characteristic impedance of the medium and the order of the mode. Under a soft seabed with low sound velocity, some modes have larger amplitudes in the water layer, becoming hydroacoustic modes, while under a hard seabed with high sound velocity, some modes have larger amplitudes in the sedimentary layer, becoming geoacoustic modes.