Abstract: In order to obtain the underwater drag reduction performance of the biopolysac-charide solution, the drag reduction characteristics of four biopolysaccharide solutions of guar gum, xanthan gum, tragacanth gum and locust bean gum were tested in the gravity circulating water tank experimental system. The influence law of the injection rate, Reynolds number and injection mass fraction on the drag reduction is shown. The results show that the four biopoly-saccharide solutions have significant spray drag reduction effects, and the locust bean gum solution has the highest drag reduction rate (14.3%). At a constant Reynolds number, with the increase of the injection rate, the drag reduction rate of each polysaccharide solution increases significantly, and shows different trends after reaching the peak value of drag reduction. The drag reduction effect of the polysaccharide solution is better when the Reynolds number is small (<2.0×10⁴). With the increase of the Reynolds number, the drag reduction law of the polysac-charide solution shows differentiation. Excessive injection mass fraction would reduce the drag reduction effect of the polysaccharide solution, and increasing Reynolds number would cause the phenomenon of “peak shift” with the increase of the mass fraction. By introducing relative injection mass fraction, the effects of the injection rate, Reynolds number and injection mass fraction on drag reduction are coupled with each other. With the increase of relative injection mass fraction, the drag reduction rate of each polysaccharide solution increases first and then decreases. Finally, based on the injection spray mass fraction, the drag reduction law of the polysaccharide solution was explained preliminarily.