The invention discloses a curve gauge with an overhead rotary knob. The curve gauge structurally comprises a base, support legs, a hand shank, the rotary knob, a screw rod, a screw cap, a string wheeland a pulling string, the top end of the hand shank is provided with the rotary knob, the center of the hand shank is provided with a through-hole in the axis direction, the through-hole is internally provided with the screw rod, the upper end of the screw rod is fixed on the rotary knob, the lower end of the screw rod is provided with the screw cap, the portion of the part, at a lower mouth portion of the through-hole inside the hand shank, of the screw rod is provided with a boss, the boss is of a disc-shaped structure and is fixed on the screw rod, the part, below the boss, of the screw rod is provided with the screw cap, the screw cap is located nearby the upper portion of the string wheel, and the screw rod can freely rotate inside the through-hole inside the hand shank. The curve gauge with the overhead rotary knob has the beneficial effects that the screw cap can be moved up and down by rotating the rotary knob, when the screw cap abuts against the string wheel to make the string wheel be fixed to be unable to rotate, so that the pulling string can not be stretched; and when the rotary knob is loosened to make the screw cap move upwards to leave the string wheel, then the string wheel can rotate under actions of the pulling string and a coil spring inside the string wheel, so that the pulling string then can be stretched and shortened.