Abstarct: Gas turbine are of equipment to generate power in powerhouses and refineries are used extensively for expenses of generating power and economic value, optimizing and enhancing the efficiency important considered issues for designers , artisans and academic people . baxsed on this , efficiency increase of gas turbines which is one of the mast fundamental power generation cycles , is of special importance , According to the subject importance , the object of this thesis is to study the methods of increasing khangiran refinery gas turbines efficiency . First , Current efficiency is evaluated and different environmental and thermodynamic factors influence (temperature and pressure, relative humidity , etc )on efficiency work of compressor , net output work energy utility factor (EUF) , Heat Rate of khangiran refinery gas turbines have been calculated Also , effect degree of nominal power and output load on gas turbines efficiency has been discussed . Relevant to performed studies , Cooling method for input air is choose as the most practical and effective way to improve efficiency and according to this various cooling methods such as evaporation cooling system , mist irrigation , absorption chillers and compressor chillers. this study consists of specification . Amount of efficiency increase and cost evaluation of each method. Finally , according to the performed studies , fogging method is selected as the best method . by choosing this efficiency increase up to 3% can be achieved and cost return cycle of performing this system is 3.2 year . At last , to use concurrent production capacity of cooling refinery consumed gas , two suggestion are presented.