The invention provides a performance and structure design method, a performance monitoring method and a structure safety monitoring method for a high-pressure cylinder and a medium-pressure cylinder of an air-cooled high-parameter steam turbine. The power and thermal performance of the high-pressure cylinder and the medium-pressure cylinder of the air-cooled high-parameter steam turbine are ensured through new technologies of steam inlet and exhaust parameter design, flow and structural size modular design, enthalpy drop optimal distribution, variable reaction degree design and the like of thehigh-pressure cylinder and the medium-pressure cylinder in the design stage. Structural safety of the high-pressure cylinder and the medium-pressure cylinder of the air-cooled high-parameter steam turbine is guaranteed through new technologies of structural design, material design, moving blade strength vibration design, rotor creep and strength and service life design, inner cylinder creep and strength and service life design, air cylinder tightness design and the like of the high-pressure cylinder and the medium-pressure cylinder in the design stage. The technical effect of optimizing and controlling the thermal performance and the structural safety performance of the high-pressure cylinder and the medium-pressure cylinder of the air-cooled high-parameter steam turbine through a designmonitoring method of performance optimization and structural improvement is achieved.