The invention discloses an underground engineering air purifier, which comprising a hole body, wherein a fixing seat is fixed above the hole body, a hydraulic cylinder, a support frame and a hydraulicpump are fixed above the fixing seat, the hydraulic pump is positioned between the hydraulic cylinder and the support frame, a water storage pool is arranged close to the support frame and above thefixing seat, the outer surface wall of the support frame is provided with an AT89S52 controller, a first fixing box is fixed on one end of the support frame, a hydraulic stretching rod is arranged below the first fixing box, a second fixing box is fixed below the hydraulic stretching rod, and a motor is installed inside the second fixing box. According to the present invention, the probes are arranged, the electric stretching rods stretch, the probes beat the inner wall of the hole body to puncture the gas bag formed by harmful gas accumulating, and the active carbon ring adsorbs the harmful gas, such that the problem that the worker touches the gas bag formed by the harmful gases during the underground drilling operation to cause the threat to the personal safety can be avoided.