Abstract: An introduction is presented to the finite element method for the strength analysis of HP inner cylinder with shrink rings in a certain type of supercritical steam turbine, based on which strength analysis and calculation of a cracked HP inner cylinder with shrink rings were conducted respectively at rated load working condition and following transient working conditions, such as in the cold start, warm start, hot start and very hot start process, etc., so as to obtain the temperature and stress distribution in the cylinder, and subsequently propose countermeasures for operation optimization of the steam turbine. Results show that the excessive stress occuring under transient working conditions is found to be one of the main causes leading to the cracking, which could be avoided by extending the rated load operation time, reducing the start-stop frequency of unit, lowering the heating rate of main steam during start-up period from 29% load to 56% load, especially for the load lying in 53%-56%.