Compressors are crucial to the efficient operation of a gas turbine; however, fouling, caused by adherence of particles to surfaces, can have a negative effect on compressor performance. In this study, a NASA Stage 35 single-stage axial-flow compressor was employed as the model for numerical simulation using the ANSYS CFX software of the effects caused by mild and severe fouling under salt fog scale. To measure these effects, two distinct models were used. For mild fouling, the simulated stator blade surface roughness was altered nonuniformly; for severe fouling, the simulated stator blade thick-ness was altered. Results indicated that surface roughness caused by mild fouling only has a small effect on compressor performance and no effect on the stable working range. However, changes in the blade thickness as a result of severe fouling have a large effect on compressor performance and a clear effect on the stability of the compressor’s working range. The fouling causes an increase in the boundary layer at the trailing edge of the suction side of the blade thereby increasing the loss of flow; fouling effect after emergence angle, wide design value, and increasing blade of circumferential stress.