A method for diagnosis of components inside a turbine generator includes collecting and measuring organic substances present in a gas inside the turbine generator to obtain data (first data). Before the collecting, organic substances generated from each component inside the turbine generator due to heat, discharge, corrosion, or friction, are measured to compile data (second data). The first data is compared to the second data to determine whether the first data includes the same data as in the second data to detect deterioration of the components inside the turbine generator.