The invention discloses unit full load denitration input achieved by an ultra-supercritical coal-fired unit through a novel starting manner and relates to the technical field of fire coal. The unit full load denitration input is achieved through the manners that (1) the economizer inlet water feeding temperature is increased, wherein a steam turbine high-low adding system is put into use before unit grid-connection so as to improve the boiler feed water temperature, furnace water circulation pump output is increased for heating economizer inlet feed water, and it is kept that the economizer inlet water feeding temperature always keeps at about 260 DEG C before the boiler dry state; (2) overheating and reheating smoke baffle adjustment and optimization are carried out, wherein the overheating and reheating smoke baffle opening degree is closed to 60% of the opening degree before unit grid-connection; and (3) boiler dry-wet state conversion optimizing is carried out, wherein the 30%BMCR load unit three-coal-mill dry-wet state conversion manner is changed into a higher-than 40%BMCR load four-coal-mill dry-wet state conversion manner. The unit full load denitration input has the beneficial effects that input into a denitration system at the denitration inlet smoke temperature higher than 300 DEG C before unit starting grid-connection, the requirement for continuous and stable running of the denitration device within the full load scope is met.