The fuel of coal-fired power plant is coal mainly，if flue gas of coal combustion after being used forheating superheated steam and reheat steam is discharged into air，it will cause pollution，such as acid rain，thisdramatic phenomenon of pollution． With the awareness of the protection of the natural environment being stronger，FGD project for flue gas which is discharged by IDF is in line with the requirement of the various countries of theworld on environmental pollution control． Temperature of original gas determines the efficiency of FGD to some ex-tent． This article describes the strategy and implementation methods of temperature control in seawater FGD whichis created in Symphony DCS system，utilizing the PADE approximation of Mathematical and optimal control of mod-ern control theory to optimize the lag temperature control，using the C language interface of Composer to configura-tion，and describing the specific implementation method． After the actual inspection in the site，this way is provedfeasible．