The adjustable chemical syringe is a very commonly used accessory in high-pressure cleaning machines. Through it, detergents, other chemical liquids, or disinfectants can be sucked in and mixed with high-pressure water flow to form a mixed liquid to enhance the dirt removal effect, or spray disinfectant. This chemical syringe is generally connected to the outlet end of the pump and has a nozzle with a smaller aperture built in. When the cleaning machine is connected to a chemical nozzle with a larger aperture, the aperture of the nozzle forms a pressure difference with the aperture of the nozzle in the syringe, which produces a siphon effect, and the one-way valve of the syringe can be opened to suck in detergents or other chemical liquids, which are evenly mixed into the high-pressure water flow to form a mixed liquid, which is sprayed from the nozzle for cleaning, dirt removal or disinfection. The suction volume of this chemical syringe is adjustable, and the suction volume can be controlled as needed by adjusting the knob to meet the user's needs. The syringe body is made of brass, which has strong corrosion resistance and is an ideal material for syringes.