Abstract: Timely detection of compressor fouling of gas turbines and removal of such fault through washing can effectively reduce operation and maintenance costs and also eliminate possibilities of other faults in gas lines. With two LM2500+SAC gas turbines for long-distance gas pipelines as examples, a calculation model for compressor performances of gas turbines based on thermal parameters of gas lines was established to analyze changes in isentropic efficiency, mass flow rate of in-coming gases and energy consumptions before and after washing of such compressors. Research results show that, after washing operations, isentropic efficiencies of two compressors enhance by 0.9% and 1.5%, respectively. However, the isentropic efficiencies decline by approximately 1% for every 2 000 h in operation and tend to be stable when the fouling on the blade surface reaches certain extent. Whenever the isentropic efficiencies decline by 1%, equivalent mass flow rate decreases by approximately 2%. Washing operations may effectively reduce energy consumption, but increases in environmental temperatures may lead to increases in energy consumption. Consequently, energy consumption may not be taken as an indicator for determining compressor fouling. Instead, reductions in isentropic efficiencies under identical compression ratios and reductions in mass flow rate of the compressor under identical rotation speed are recommended as such indicators.