1 unit in Huaneng Yuhuan Power Plant is the first 1 000 MW ultra-supercritical unit in China. This paper introduced the first maintenance of IP cylinder in this unit and analyzed the deformation of inner and outer cylinder. The effective treatment scheme for IP inner cylinder deformation was proposed: the bolt in the horizontal joint of cylinder being repeatedly, alternately heated and cooled； the IP cylinder being reassembled without the friction and collision between dynamic and static component, after repeated measuring and testing. After the cylinder maintenance, it succeeds in one time to turning and starting turbine, and makes a success in loading operation, which shows that the treatment scheme is accurate and reliable.