Abstract: In order to study the dynamic characteristics of the water wall outlet parameters of ultra-supercritical boiler, the calculation model of the dynamic characteristics of the water wall system under supercritical pressure was established by using the frequency domain method. The experimental results show that the calculated values are in good agreement with the measured data. The lower furnace water wall of an ultra-supercritical boiler was calculated, and the dynamic characteristics under 75%THA load were obtained. The dynamic characteristics at heat flux, inlet enthalpy, inlet mass flow rate and outlet pressure step were studied. The effects of heat flux, inlet enthalpy, inlet mass flow, and outlet pressure step on the outlet fluid parameters were analyzed separately. Results show that the response time due to disturbance decreases when the inlet enthalpy, inlet mass flow rate, and heat flux increases; the response time due to disturbance increases when the inlet pressure and pipe section length increase.