The invention discloses an active screw compressor gas pulsation attenuating device which is a gas pulsation attenuating flange composed of an exhausting orifice flow pass and a branch flow pass. One end of the gas pulsation attenuating flange is connected with a screw compressor exhausting flange, the other end of the gas pulsation attenuating flange is connected with an exhausting bearing pedestal, exhausting of a screw compressor is divided into two ways, a gas pulsation of one way flows in from an inlet of the exhausting orifice flow pass and flows out from an outlet of the exhausting orifice flow pass, a gas pulsation of the other way flows in from an inlet of the branch flow pass and flows out from an outlet of the branch flow pass, and then the gas pulsations of the two ways are combined into one to be exhausted into an exhausting bearing pedestal flow pass. According to the operation working condition of the screw compressor, the length difference between the exhausting orifice flow pass and the branch flow pass of the gas pulsation attenuating flange is determined to enable the gas pulsations of the two ways to generate the 180-degree phase difference when the gas pulsations are converged in the exhausting bearing pedestal flow pass, the gas pulsations of the screw compressor are attenuated actively from the source, and vibration noise of the screw compressor is reduced. The active screw compressor gas pulsation attenuating device is simple in structure, high in manufacturing and installing operability and good in vibration and noise reduction effect.