The demand for high-capacity, anti-interference, safe and reliable transmission between ships on the sea and between ships and aircraft is becoming urgent. Terahertz band has a high frequency band and large bandwidth, making it an excellent means of high-capacity transmission and anti-interference communication. Based on the characteristics of marine terahertz communication, the influence of water vapor attenuation on terahertz wave on the sea surface in China is analyzed firstly. Then, based on the link budget and propagation reliability calculation, a marine terahertz communication system is designed. After being tested on a 150 m river, the system's feasibility is verified by achieving a speed of 520 Mbps with an bit error rate of 2×10⁻⁸.