<p> Autonomous Underwater Vehicles (AUVs) are used to survey undersea resources in seawater. Research is underway to integrate wireless power transmission capabilities into AUVs, where the freedom of not being tethered by a wire enhances their operational efficiency. However, seawater has varying salinity and electrical conductivity, which can affect power transmission efficiency. This paper investigates the influence of salinity on a wireless power transmission system in seawater operating at a frequency of 85 [kHz]. To investigate the power transmission in experiments, a single-wire solenoid coil with waterproofing is designed. Experimental results show that increased salinity leads to higher power loss and a decrease in transmission efficiency, which decreased significantly with higher salinity. Furthermore, computer simulations using magnetic field analysis software measure magnetic flux density, the number of flux chains, main flux, and leakage flux. From magnetic field analysis, when the salinity is increased, the magnetic flux density, the number of flux chains, the main flux, and leakage flux decreased. This was also found to be a factor in lower power efficiency.</p>