Abstract: In the DCS system of supercritical coal-fired units, the quality requirements of main steam are very strict, so the control of main steam parameters is very important during the load changing period of units. In this paper, the main steam control loop of 660MW supercritical unit of XXXX Power Plant is optimized in detail, so as to achieve the goal of stable main steam parameters during the unit load changing period, and effectively ensure the safe and economic operation of the unit, for reference by peers in the industry.