The invention relates to a complex working condition monitoring device for well drilling. The device comprises a liquid inlet pipe, a liquid outlet pipe, an upper cover, a sliding piston and an air bottle; a flange is arranged at one end of the liquid inlet pipe, and external threads are arranged at the other end of the liquid inlet pipe; the inner diameters of the liquid inlet pipe are different in the axial direction, a ventilation hole is formed in the upper end of the liquid inlet pipe, an erosion prevention liner pipe is arranged in the liquid inlet pipe, the upper cover is in threaded connection with the liquid inlet pipe, a small pneumatic cylinder and a small air pressure cavity pressure sensor are installed at the center of the upper cover, an air filing hole of the upper cover is connected with the air bottle through an air pipeline, the sliding piston is formed by a large piston body and a small piston body, the small piston body slides in the small pneumatic cylinder, and the large piston body slides horizontally in the liquid inlet pipe. According to the complex working condition monitoring device for well drilling, the area difference between the large piston body and the small piston body is used, flowing pressure, exerted on the large piston body, of drilling liquid in the flowing process of the drilling liquid is amplified, the pressure sensor is used for monitoring changes of the pressure of the air in the small pneumatic cylinder, and the device is simple to install, convenient to adjust, wide in adjustment range, high in sensitivity, safe and reliable to use and capable of meeting early-stage monitoring requirements.