A torsion-adjustable impact wrench, includes a housing, a powering unit including an impact mechanism configured to generate an intermittently increasing torque, an adjusting unit configured to manually set a first torsion value and generate a corresponding a first torsion signal, a detecting unit configured to detect a rotational speed of the powering unit and generate a corresponding first rotational speed signal, and a control unit configured to generate a control signal for controlling the output of the rotational speed of the powering unit. The control unit generates a second rotational speed signal according to the first torsion signal outputted by the adjusting unit, compares the first rotational speed signal with the second rotational speed signal, and generates a control signal enabling the rotational speed of the powering unit to approach the second rotational speed.