The invention discloses a downhole supercharging device, aiming to overcome defects that existing superchargers used in petroleum drilling operation are complicated in structure, high in manufacturing difficulty, high in cost and the like. The downhole supercharging device is characterized in that a supercharging string (10) is arranged between a casing (7) and a driller string (4), an annulus is reserved between an inner bore of the supercharging string (10) and the outer circle of the driller string (4), and another annulus is reserved between the outer circle of the supercharging string (10) and an inner bore of the casing (7). A supercharging casing (3), a cavity (1) and another supercharging casing (3) of the supercharging string (10) are sequentially fixedly connected from top to bottom, a packer mounted on the supercharging casing (3) below the cavity (1) is used for packing the annulus between the supercharging string (10) and the casing (7), and the annulus inside the cavity (1) and the annulus outside the cavity (1) are communicated by a supercharging water hole fixedly mounted on the cavity (1). The downhole supercharging device has the advantages of simple and reasonable structure and capability of increasing circulation speed of downhole liquid and improving rock breaking and sand carrying capacity on the premise of not changing rated pressure of a ground pumping pressure system.