Abstract: A surgical tool for piercing tissue of a body comprises a hollow external component (1) having a peripheral wall (11), an internal component (2) movable disposed inside the external component (1) and having a piercing head (21); when the piercing head (21) and the internal component (2) retract relative to the external component (1), the movable component (3) deforms partially, expands outwardly in a radial direction, and fills the bladder (6). The movable component can be deformed to expand outward in the radial direction, so as to make the bladder to expand, so that the surgical tool can be positioned on the body of the patient.