The utility model relates to an internal curve hydraulic pump or motor with adjustable, it includes coaxial coupling and pivoted stator and rotor relatively, and the inner wall of stator is separatedeach other by a plurality of concave curved surfaces and a plurality of convex curved surface and sets up and forms, has the piston hole on the rotor, and the inner wall that is provided with a tip and stator in the piston hole contacts just another tip and follow the piston assembly that reciprocating motion was to the piston hole axial in this piston hole. In the axial orientation of perpendicular stator, an end section of the inner wall of stator be circular, and other end cross -section be concave and convex fluctuation's wave, and inner wall from its one end to its other end, and the waveconcave and convex fluctuation degree in cross -section is the grow gradually, offers on the inner wall along a plurality of guide ways of wave undulation, and piston assembly's one end position is in the guide way, and the shape of this tip and guide way matches. In the plane at the axial lead of piston hole and the crossing place of axial lead of rotor, the axial lead of piston hole and rotor radially be a contained angle.