Method for monitoring a status of a reduction gear of a gas turbine implemented by a computer and comprising, for at least one duty cycle of the reduction gear: - a step of obtaining at least one set of measurements of a plurality of parameters accomplished over at least one time interval of a determined duration during at least one operating phase of the gas turbine, said parameters comprising the operating parameters of the reduction gear including temperatures of a lubricating oil of the reduction gear at the inlet and at the outlet of the reduction gear, and of the gas turbine including at least one parameter representing a speed of the gas turbine, as well as at least one context parameter representing an environment in which said reduction gear is located; - a step of selecting, among said at least one set of measurements obtained for said at least one operating phase, of a set containing measurements that are stable with regard to a predetermined stability criterion; - a step of normalizing temperatures of the lubricating oil at the inlet and at the outlet of the reduction gear of the set of selected measurements by using the measurements of the context parameters of the set of selected measurements; - a step of evaluating, based on the set of selected measurements in which said temperatures of the lubricating oil have been normalized, a thermal efficiency of the reduction gear by using a physical model defining the thermal efficiency based on a difference between the temperature of the lubricating oil at the outlet of the reduction gear and the temperature of the lubricating oil at the inlet of the reduction gear; said monitoring method also comprising: - a step of comparing the thermal efficiency evaluated for said at least one duty cycle of the reduction gear with respect to at least one reference signature representing an operational behavior or a faulty behavior of the reduction gear; and - a step of determining a status of the reduction gear depending on the result of the comparison step. - a step of obtaining at least one set of measurements of a plurality of parameters accomplished over at least one time interval of a determined duration during at least one operating phase of the gas turbine, said parameters comprising the operating parameters of the reduction gear including temperatures of a lubricating oil of the reduction gear at the inlet and at the outlet of the reduction gear, and of the gas turbine including at least one parameter representing a speed of the gas turbine, as well as at least one context parameter representing an environment in which said reduction gear is located; - a step of selecting, among said at least one set of measurements obtained for said at least one operating phase, of a set containing measurements that are stable with regard to a predetermined stability criterion; - a step of normalizing temperatures of the lubricating oil at the inlet and at the outlet of the reduction gear of the set of selected measurements by using the measurements of the context parameters of the set of selected measurements; - a step of evaluating, based on the set of selected measurements in which said temperatures of the lubricating oil have been normalized, a thermal efficiency of the reduction gear by using a physical model defining the thermal efficiency based on a difference between the temperature of the lubricating oil at the outlet of the reduction gear and the temperature of the lubricating oil at the inlet of the reduction gear; - a step of comparing the thermal efficiency evaluated for said at least one duty cycle of the reduction gear with respect to at least one reference signature representing an operational behavior or a faulty behavior of the reduction gear; and - a step of determining a status of the reduction gear depending on the result of the comparison step.