Terahertz (THz) technology, due to its unique non-contact measurement and non-destructive testing capabilities, has shown remarkable potential in a wide range of marine applications. The ability to detect pollutants, assess the condition of marine infrastructure, and monitor ecological health in real time offers significant advantages over traditional methods. As such, THz technology holds great promise for advancing marine environmental protection and resource management. Firstly, the application of terahertz (THz) waves in marine environment monitoring is first introduced. In the THz waveband, the normalized radar cross section (NRCS) is used to measure variations in reflection intensity at different incident angles, which helps evaluate the characteristics of the oil film. NRCS reflects the interaction of THz waves with the oil film surface, providing insights into its thickness, distribution, and surface properties. As the propagation properties of THz waves differ between the oil film and the water surface, factors such as the thickness, composition, and surface conditions of the oil film directly influence the reflection characteristics. By measuring the reflection intensity at different incident angles, detailed information about the oil film can be obtained, allowing for precise assessment of its thickness and distribution (Fig.5). For water quality classification, THz waves are incident at a specific angle onto an ATR prism, generating evanescent waves that penetrate the sample through total reflection. Fourier transform is applied to extract the reflection coefficient and calculate the complex permittivity. Optical parameters are modeled and classified to achieve water sample classification (Fig.6-Fig.7). Next, the application of THz technology in marine non-destructive testing is introduced. This part is divided into three sections: non-destructive testing of ship hull fiberglass materials, protective coatings and paint layers, and PE pipes. Non-destructive testing of ship hull fiberglass materials (Fig.8, Fig.10-Fig.11) and PE materials (Fig.16-Fig.17) is carried out using THz time-domain spectroscopy (THz-TDS). The principle involves exciting THz pulses to pass through the sample, collecting transmitted and reflected signals. By sampling these signals in the time domain and applying Fourier transform, the data is converted into the frequency domain, creating imaging for internal structure and defect visualization. This process enables the non-destructive evaluation of internal features and defects. For the non-destructive testing of ship protective coatings and paint layers (Fig.12-Fig.14), time-domain THz technology is used to record the time delay and amplitude variations of reflected signals. Deconvolution techniques are applied to calculate the coating thickness, and stationary wavelet transform (SWT) is utilized to extract characteristic signals for internal defect identification. Finally, the application of THz technology in marine ecosystem monitoring is discussed. This includes the detection of microalgal and microbial metabolites (Fig.18-Fig.20) to assess the potential for ecological issues, such as red tide phenomena, and the detection of radioactive cesium ions in seawater (Fig.22). The use of THz waves in marine ecosystem monitoring offers a promising approach for early detection of ecological disruptions and contamination in aquatic environments. The results shown in Fig.18 and Fig.22 highlight the potential of THz technology in enhancing marine environmental monitoring, ensuring a safer and more sustainable marine ecosystem. THz technology has demonstrated substantial potential in various marine applications, particularly in pollution detection, material integrity assessment, and ecological monitoring. Its non-contact and non-destructive characteristics make it an ideal tool for safeguarding marine infrastructure and ecosystems. As THz technology continues to evolve, its applications in the marine field are expected to expand, offering more efficient and accurate methods for real-time monitoring and early warning systems. In the future, THz technology is poised to play a crucial role in marine resource protection, contributing to sustainable marine management and environmental conservation.