Air-extracting device of compressor

The utility model relates to an air-extracting device of a compressor, comprising a motor, one end of the motor is connected with a crankcase I through a coupler, and the crankcase is provided with sections of cylinder bodies: the fourth section, the fifth section, the sixth section, and the seventh section; the characteristics are as follows: the other end of the motor is connected with a crankcase II through the coupler, and the crankcase II is also provided with the sections of cylinder bodies: the fourth section, the fifth section, the sixth section, and the seventh section. The utility model solves defects of too-high outlet pressure and large safety hazard of the section caused by that the air-extracting device of the three-level compressor is adopted in the synthetic ammonia production, and has advantages of safe and reliable using, and small output pressure of the section.