To provide a corrosion protection controlling system for a plant, which automatically controls the injection quantity of a corrosion inhibitor based on a mathematical model.

This system comprises a database means for accumulating historically several data of measured values for physical quantity having a cause-effect relationship with corrosion environment factors of an object plant for a corrosion protection control, input materials, subgroup data of controlling parameters, and the like, a mathematical model producing means for statistically processing the data of the database means, an estimating means of corrosion deterioration in the plant based on the above mathematical model, a corrosion protecting controlling controller means for operating by output of the estimating means, and a distributed type controlling means for controlling in real time the injected quantity of the corrosion inhibitor into the above object plant for corrosion protection control based on the control output of the controlling means.