The invention provides an underactuated variable-stiffness manipulator based on variable-stiffness elastic joints, relates to a variable-stiffness manipulator, and aims to solve the problem about application limitations of a stiff manipulator and a flexible manipulator in the prior art. The underactuated variable-stiffness manipulator comprises the three variable-stiffness elastic joints, and further comprises a palm, a motor, a base, supporting columns and three fingers, wherein the three fingers comprise one flexion-extension finger and two coupling rotary flexion-extension fingers; the palmis arranged above the base; the palm and the base are connected through the supporting columns; the vertically-arranged motor and the three variable-stiffness elastic joints are mounted on the base;the flexion-extension finger and the two coupling rotary flexion-extension fingers are arranged on the palm along the circumferential direction of the palm; through a steel wire rope, the two couplingrotary flexion-extension fingers are driven by an output shaft of the motor to perform rotary motion; output shafts of the three variable-stiffness elastic joints are arranged in a one-to-one correspondence manner; and the flexion-extension motion of the flexion-extension finger and that of the two coupling rotary flexion-extension fingers are driven through the steel wire rope. The underactuatedvariable-stiffness manipulator provided by the invention belongs to the field of robots.