The invention discloses a hydraulic expander. The hydraulic expander comprises cylinder bodies, wherein a plurality of ring-shaped slots are formed in the radial direction of each cylinder body; a piston is arranged in each ring-shaped slot; oil paths are arranged on the cylinder bodies below the pistons; the ring-shaped slots communicate with the oil paths; a long slot which penetrates through the two ends of each cylinder body is formed in the axial direction of the corresponding cylinder body; the long slots are positioned above the pistons; jacking bars which abut against the pistons are restrained in the long slots; cylinder bodies positioned at the two ends of each jacking bar are provided with fixed blocks which are restrained in the long slots; the two ends of each jacking bar are provided with inclined parts; and the inclined parts extend towards the fixed blocks in an inclined mode from one side, far from the pistons, of the corresponding jacking bar. The hydraulic expander is high in safety, and does not damage the environment. During work, the plurality of the pistons act together to generate great working energy, so that capacity of decomposition is greatly improved. Compared with the conventional hydraulic expander, the decomposition time is greatly shortened, so that the working efficiency is effectively improved.