The modern gas turbine engine has been used in current power generation industry for almost half a century.Gas turbines are designed to operate with the best efficiency during normal operating conditions and at specific operating points.However,the real world is non-optimal and the engine may have to operate at off-design conditions due to load requirements,different ambient temperatures,fuel types,relative humidity and driven equipment speed.Also more and more base-load gas turbines have to work today on partial load too,which can affect the hot gas path condition and life expectancy.At these off-design conditions,gas turbines efficiency and life deterioration rate might significantly deviate from the design specifications.During a gas turbines life,power generation providers might need to perform several overhauls or upgrades for their engines.Thus,the off-design performance after the overhaul also might be changed.Prediction of gas turbines off-design performance is essential to economical operation of power generation equipment.In this paper,an integrated system for complex design and off-design performance prediction(AxSTREAM? Platform)is presented.It allows to predict gas turbine engines design and off-design performance almost automatically.Each components performance such as turbine,compressor,combustor and entire secondary flow(cooling)system is directly and simultaneously calculated for every off-design performance request,making possible to build an off-design performance map including cooling system.The example of off-design performance estimation of industrial gas turbine engine is presented.The presented approach provides wide capabilities for optimization of operation modes of industrial gas turbine engines and other complex turbomachinery systems for every specific operation conditions(environment,grid demands and other factors).