A seal for a repeatedly switchable stepless fracturing sliding sleeve includes a C-ring, and two A-rings, two jackets and two B-rings symmetrically provided in sequence on two sides of the C-ring in an axial direction. A mounting cavity open in a direction away from the C-ring is formed in the jacket, and a U-shaped leaf spring is provided therein. The A-ring covers a supporting lip of the jacket and has a protruding portion extending into the mounting, and the A-ring is provided with a through hole allowing the mounting cavity to be in communication with an external fluid. When the whole seal is pressed forwardly or reversely by the fluid, the supporting lip can support and tightly abut on the A-ring, and the external fluid can enter the mounting cavity via the through hole and provide a pressure for a sealing lip to tightly abut on a sealing surface.