Abstract: A proposal was suggested for maintenance interval optimization of steam turbines based on the design life, while an introduction was presented to the statistical results of utilization hours for domestic thermal power units, the calculation methods for common equivalent operating hours, the maintenance interval of steam turbines obtained based on the first equivalent operating hours, the calculation methods for start weight coefficients and load change weight coefficients of steam turbines based on the design of fatigue and creep life, the calculation methods for the second equivalent operating hours, the optimization methods for the maintenance interval, the calculation methods for annual average life expenditure of steam turbines and the calculation methods for annual average grade maintenance cost of a unit, together with application examples of a 1 000 MW ultra-supercritical steam turbine and a 600 MW supercritical steam turbine. Results show that compared with the two standards in China Power Industry, the number of years for class A maintenance interval of steam turbines optimized based on the design life is larger, with less average annual life expenditure of the steam turbine and lower average annual grade maintenance cost of the unit. This may serve as a reference for safety and economic operation of power plant steam turbines.