<p>This study investigates inductively coupled transmission technology using seawater and underwater anchor chains as the transmission medium for real-time data transfer from underwater measurement instruments. Because of the physical properties of seawater, challenges, such as frequency selective fading and multipath effect, limit long-distance current signal transmission. Conventional modulation techniques, such as amplitude shift keying (ASK) and differential phase shift keying (DPSK), are constrained by low bandwidth utilization and high bit error rates (BER). To address these issues, we optimize the seawater channel model using data from the National Oceanographic Data Center and previous measurements, analyzing the relationship between seawater conductivity, depth, and signal frequency. We constructed an experimental platform using a six-winding manganese-zinc ferrite ring based on an inductive coupling model for data transmission. A steel cable is anchored at both ends of a seawater bucket through two rings, exposing the cable core to establish a closed loop in seawater. An orthogonal frequency division multiplexing (OFDM) algorithm is used to improve transmission performance by distributing data across multiple subcarriers, effectively mitigating multipath fading and frequency selective fading. Compared with ASK and DPSK, this method significantly reduces the BER and improves the channel capacity, exhibiting robustness in underwater communication. Finally, in our study, a mathematical model of the underwater multipath channel for distances of 300, 1000, and 2000 m is established, showing an improvement in channel capacity of approximately 2.5 bps/Hz based on the OFDM algorithm. This advancement is essential for enhancing the performance of underwater signal transmission and supporting its practical application.</p>