A gas turbine control method for controlling a gas turbine plant with a gas turbine, the method comprising steps of: detecting combustion vibrations occurring in each combustor of the gas turbine, components or calorific value of fuel supplied to the combustor, and other process variables including process variables regarding fuel and air supplied to the combustor, which affect the combustion vibrations; formulating mathematical formulae for mathematically modeling combustion vibration characteristics on a basis of the process variables obtained in the detecting step; and increasing and decreasing flow rate of the fuel or the air supplied to the combustor so as to maintain an operation condition under which the combustion vibrations are unlikely to occur, based on the mathematically modeled combustion vibration characteristics; further comprising the steps of: storing each of said process variables into a plurality of databases depending on the detected values, of the components or the calorific value of the fuel, wherein said process variables are stored into the plurality of databases such that at least two databases have a common interval which is an area where a boundary region of each of the two databases having data regarding the components or the calorific value overlap; setting a threshold value in the common interval; and retrieving the detected values of the components or the calorific value of the fuel from each database with the detected values of the other process variables to perform approximation treatments of the combustion vibration characteristics; wherein, regarding the data in the common interval of the two databases, data is retrieved from the common interval of the database depending on the threshold value and the approximation treatments are performed on the retrieved data so as to decrease discontinuity in mathematically modeling the combustion vibration characteristics in a process of the approximation treatments. detecting combustion vibrations occurring in each combustor of the gas turbine, components or calorific value of fuel supplied to the combustor, and other process variables including process variables regarding fuel and air supplied to the combustor, which affect the combustion vibrations; formulating mathematical formulae for mathematically modeling combustion vibration characteristics on a basis of the process variables obtained in the detecting step; and increasing and decreasing flow rate of the fuel or the air supplied to the combustor so as to maintain an operation condition under which the combustion vibrations are unlikely to occur, based on the mathematically modeled combustion vibration characteristics; storing each of said process variables into a plurality of databases depending on the detected values, of the components or the calorific value of the fuel, wherein said process variables are stored into the plurality of databases such that at least two databases have a common interval which is an area where a boundary region of each of the two databases having data regarding the components or the calorific value overlap; setting a threshold value in the common interval; and retrieving the detected values of the components or the calorific value of the fuel from each database with the detected values of the other process variables to perform approximation treatments of the combustion vibration characteristics; wherein, regarding the data in the common interval of the two databases, data is retrieved from the common interval of the database depending on the threshold value and the approximation treatments are performed on the retrieved data so as to decrease discontinuity in mathematically modeling the combustion vibration characteristics in a process of the approximation treatments.