The temperature deviation is an inherent issue in large-scale tangentially fired pulverized-coal boilers.This article investigates numerically the forming mechanism of gas velocity and temperature deviations from the perspective of nonlinear flow characteristics in an ultra-supercritical utility boiler.Firstly,the cold state simulations of two-dimensional and three-dimensional models of furnace are performed.With the increase of Reynolds number from burner nozzles,the temperature and velocity distributions in furnace show the trend of symmetrical,slightly asymmetrical,and completely asymmetrical.The generated tangential radius of flow becomes larger and declining.It is concluded that the nonlinear flow characteristics is the key issue for the velocity and temperature deviations in the tangentially fired pulverized-coal boiler furnace.Secondly,the full combustion simulation is carried out under BMCR (Boiler Maximum Continuous Rating) conditions and validated by experimental measurement.It is also found that the centre of tangent circle becomes larger along the height of the boiler furnace and deflects though the burner structure and boundary conditions are absolutely symmetrical.The temperature and velocity distributions are asymmetrical under BMCR conditions.Due to the nonlinear flow,it inevitably brings the residual swirling flow at the upper furnace zone which is one origin of temperature deviation of the gas after the furnace exit.