The cause of large reheat steam temperature deviation is analyzed for a 700MW tangentially low NOxutility boiler

and the experimental investigation of the influence of bias parameters setting of additional air（ AA） in vertical tilt angle and opening on reheat steam temperature deviation is carried out. The results shows that the residual rotation momentum has caused the gas temperature and velocity deviation in the plate zone and the horizontal flue gas pass

which eventually leads to the temperature deviation of reheated steam. The bias setting of the vertical tilt angle and opening of AA can effectively reduce the temperature deviation of re-heated steam. For Shenhun coal used in the experiments

the temperature deviation of re- heated steam can be controlled less than 4 ℃.