For the measurement of seawater low conductivity environments such as salty tide, this paper proposes a single-coil measurement model based on magnetic resonance and eddy current technology. An equivalent coupled circuit model of seawater eddy current applicable to single-coil magnetic resonance is established, and the specific influence of eddy current loss on the circuit parameters is theoretically analyzed. The influence of series and parallel resonance on seawater conductivity measurement is investigated by comparing theory and simulation, and it is proved that the variation of the imaginary part of the voltage of the parallel load is more stable than that of the series resonance. The single-coil seawater conductivity measurement system was built for laboratory tests, and the test results show that the loop resonance has an obvious enhancement effect on seawater eddy currents, the load voltage at resonance varies linearly with the growth of conductivity, and the parallel resonance method is better than the series resonance method in the measurement. The magnetic resonance single-coil model has the feasibility of seawater conductivity measurement and has a good development prospect in the direction of low conductivity, non-contact sensors.