The range of main steam parameters had been chosen

the power-generating efficiency and flue gas quantity corresponding to different main steam parameters being calculated by programming

and the curves which reflect their relationship being given.Results show that the flue gas quantity reduces along with increase of initial temperature and initial pressure.When the initial pressure(or initial temperature) varying in a certain range

the higher the initial temperature(initial pressure) is

it is more useful to reduce the flue gas quantity.Some economic parameters of subcritical unit have been compared with the ultra-supercritical unit of same equiped capacity

the result proves that the enhancement of unit's main steam parameters can increase the environmental protection profit.