A new high-efficiency ocean thermal energy conversion (OTEC) system using non-azeotropic mixed working fluids with two regenerative cycles is proposed. Based on the first law of thermodynamics, a numerical calculation model for the proposed cycle was established to study the effects of the mass fraction of mixed working fluids, turbine inlet pressure and seawater temperature on the performance of the cycle system. An experimental plant of the proposed OTEC system was established to study the effects of seawater temperature and turbine inlet pressure on the cycle thermal efficiency. The results show that the cycle thermal efficiency and net output power of the system both increase with a decrease in cold seawater temperature or an increase in warm seawater temperature. The system cycle thermal efficiency and net output power both initially increase and then decrease with an increase of the working fluid mass fraction. The system cycle thermal efficiency and net output power both initially increase and then decrease with an increase of the turbine inlet pressure under a certain working fluid mass fraction. The experimental results of cycle thermal efficiency with various performance parameters were basically consistent with the theoretical analysis results; however, the experimental values were lower than the theoretical analysis results.