The invention provides a trunk injector for injecting a disease-treating chemical into a trunk. The trunk injector comprises a screw rod, spring seats, a slider, a chemical adding tank, a driven shafttube and a threaded connecting sleeve and is characterized in that a first rotary shaft and a second rotary shaft are respectively connected to two ends of a double-shaft motor, the screw rod is connected to the first rotary shaft, the spring seats are respectively arranged on the first rotary shaft parts located at two ends of the screw rod, a push rod at the top of the slider penetrates a slidegroove in an injector body to be arranged on the rear side of a piston rod, the inner side of a transparent chemical tube is provided with a rubber plate and the piston rod, a sealing partition is further embedded into the inner side of the front end of the transparent chemical tube, five arc-shaped brushes are connected to one end, penetrating the sealing partition, of the driven shaft tube, a drill bit is connected to one end, penetrating the transparent chemical tube, of the driven shaft tube through the threaded connecting sleeve, a hand wheel sealing column penetrates the middle of the threaded connecting sleeve, and the chemical adding tank is connected to the top of the transparent chemical tube through a pipeline. The trunk is capable injecting the chemical into the trunk during drilling.