Abstract: Based on the system modelling with AFT software, for the reheat steam piping with the traditional double-piping layout in an ultra-supercritical unit, researches were conducted on the temperature change of the two sides of left and right outlet pipes in the boiler header, and the influence on the steam temperature and pressure parameters of the two sides of left and right inlet pipes in steam turbine, while corresponding optimization schemes were proposed. Research results show that, the steam temperature deviation could not be controlled with the application of the traditional double-piping layout, while the steam temperature deviation of steam turbine two sides could be well controlled by the optimized double-piping layout with mixing temperature design, which is conductive to the safe and reliable operation of steam turbine.