Method for controlling an injector intended for injecting a pollution-control liquid additive into the exhaust gases of an internal combustion engine at a flow rate governed by a given frequency and opening time of the injector, the injector having a calibration curve that establishes, at given frequency, pressure, temperature and nature of the liquid, the amount of liquid injected during an opening of the injector as a function of the duration of this opening, this curve comprising at least one linear zone (calibration line) and a non-linear zone, said method being characterized in that in the linear zone the parameters of the calibration line are used and in the non-linear zone use is made of a set opening time and a variable frequency according to at least one calibration point established for this purpose. SCR system to which this method can be applied.