Compressor is a kind of equipment used to increase gas pressure. It has a wide range of applications in engineering, such as power machinery, ventilation and blast engineering, refrigeration engineering, chemical industry, diving operations, medical treatment and other industries. In this lecture, the classification and working principle of compressors are introduced. The power consumption of the compressor is analyzed and calculated when the quantitative gas is compressed from the same initial state to the predetermined final pressure. The variety methods of power saving and energy saving of the compressor should be further analyzed. Finally the attention points are introduced for the real appliction of specific compressors.