1. In a method for controlling a wet lime-gypsum process desulfurization plant, wherein an absorption tower is provided which desulfurizes an exhaust gas by bringing an incoming exhaust gas into contact with an absorbant liquid circulated therethrough by means of a plurality of pumps, the improvement wherein a pH value of the absorbent liquid and a number of working pumps value are set according to the amount of the exhaust gas load of said absorption tower referring to set values which determines the lowest pH value of the absorbent liquid and the minimum number of working pumps for a given amount of desulfurization for each gas load, wherein said set values are prepared by performing a process simulation, and the feed rate of the absorbent liquid and the number of working pumps are controlled on the basis of said set values, and in which said process simulation is created by providing first and second simulation models, in the first simulation model the pH value of the absorbent liquid and the desulfurization ratio are calculated on the basis of the exhaust gas flow rate, the inlet SO.sub.2 concentration, the absorbent liquid circulations flow rate and the feed rate of a neutralizing agent of the absorbent liquid, these calculated values are compared with the detected values of the pH value and the desulfurization ratio during operation, a reaction constant set within the first and second simulation models is corrected on the basis of deviations between the compared values, and said set values are thus created by the corrected second simulation model, whereby economy and capability to accept variation of the load of said plant are improved.