Abstract: Taking the 650 MW supercritical boiler in a power plant as an example, to guarantee safety operation of the boiler during deep peak regulation process, a calculation model for flow and pressure of the water wall was established by equivalent loop method, while a heat load model was set up for a single tube in the spirally wound tubes, based on which, hydrodynamic characteristics of the water wall were calculated under ultra-low load conditions, and subsequently the outer wall temperature distribution at outlet of the spirally wound tubes and the mass velocity distribution of tubes in the upper and lower furnace were obtained. Based on the verified model, calculations and analyses were conducted on hydrodynamic safety of the water wall under 30% boiler maximum continuous rating（BMCR）. Results show that the curve of pressure drop and mass flow in the spirally wound tubes of the supercritical boiler exhibits a one valued feature under 30% BMCR, and the pulsation of the tubes lies in a stable region with a large margin.