Abstract: Marine current power generator works under the current, so its working environment is worse than wind power generator, such as sea water corrosion, sealing problems etc., once the marine current power generator breaks down, lifting maintenance is difficult and the cost is very high, so it is necessary to analyze the reliability of the marine current power generator. Reliability model of the generator is established and parts stress analysis is used to predict its reliability. Considering the permanent magnet failure is the specific failure of permanent magnet generator and the irreversible demagnetization of permanent magnet occurs easily under high temperature, the magnetic-thermal coupling simulation for the generator is conducted and the effect of size parameters on the temperature of the permanent magnet and the life of the generator is analyzed.