A flushing system for a toilet, comprising: a flush valve including a valve base; a linear control water drainage mechanism, disposed above the valve base, and having a hollow body and a rope connected to a metal block; and a piston, movably disposed in the hollow body for reciprocation, having a central partition plate in the hollow body for dividing the hollow body into an upper portion and a lower portion, the upper portion and the lower portion being a piston control chamber and a water drainage fluid chamber respectively, and the water drainage fluid chamber being configured to apply water pressure to the piston; wherein a sealing rubber is disposed under the piston, a hydraulic water drainage mechanism is disposed beside the linear control water drainage mechanism, a torsion spring is axially disposed in the piston control chamber against the central partition plate, the torsion spring pushes the piston to move downward when no water pressure exists so that the sealing rubber seals the valve base, the hydraulic water drainage mechanism includes an immersible pump including an inlet communicating with a reservoir and an outlet communicating with the water drainage fluid chamber, when the immersible pump is activated it draws water from the reservoir into the water drainage fluid chamber through the outlet of the immersible pump so as to make water pressure in the water drainage fluid chamber to lift the piston with the torsion spring compressed so that water in the reservoir flows through the valve base to flush; when the flush valve is in a closed state, the valve base is sealed by the sealing rubber, when the rope is pulled to lift the metal block and the piston, the piston moves upward to compress the torsion spring, such that water in the reservoir 28 flows through the valve base to flush. a flush valve including a valve base; a linear control water drainage mechanism, disposed above the valve base, and having a hollow body and a rope connected to a metal block; and a piston, movably disposed in the hollow body for reciprocation, having a central partition plate in the hollow body for dividing the hollow body into an upper portion and a lower portion, the upper portion and the lower portion being a piston control chamber and a water drainage fluid chamber respectively, and the water drainage fluid chamber being configured to apply water pressure to the piston; wherein a sealing rubber is disposed under the piston, a hydraulic water drainage mechanism is disposed beside the linear control water drainage mechanism, a torsion spring is axially disposed in the piston control chamber against the central partition plate, the torsion spring pushes the piston to move downward when no water pressure exists so that the sealing rubber seals the valve base, the hydraulic water drainage mechanism includes an immersible pump including an inlet communicating with a reservoir and an outlet communicating with the water drainage fluid chamber, when the immersible pump is activated it draws water from the reservoir into the water drainage fluid chamber through the outlet of the immersible pump so as to make water pressure in the water drainage fluid chamber to lift the piston with the torsion spring compressed so that water in the reservoir flows through the valve base to flush; when the flush valve is in a closed state, the valve base is sealed by the sealing rubber, when the rope is pulled to lift the metal block and the piston, the piston moves upward to compress the torsion spring, such that water in the reservoir 28 flows through the valve base to flush.