The invention provides a pre-tightening force adjusting device and method of a tension guiding mechanism, and belongs to the technical field of aerospace assembly. The to-be-adjusted tension guiding mechanism is fixed to one side of a fixing seat of the adjusting device, and thus a rotating shaft of the tension guiding mechanism and a rotating shaft of the adjusting device are fixedly connected; arotating wheel is rotated to drive a volute spring of the tension guiding mechanism to be tightly coiled or uncoiled; when the preset position is reached, braking is conducted through a brake, and the volute spring is always in the current state to achieve pre-tightening of the plane volute spring; torque is measured through a torque wrench, and by combining with the positions of clamping grooveswhich are evenly distributed in the circumference, the working position of the plane volute spring when a solar battery array is expanded can be accurately found; and the pre-twisting angle of the plane volute spring is precisely set to be +/- 5 degrees, the output torque is precisely controlled to be +/- 0.04 Nm, and the adjusting efficiency and accuracy of the tension guiding mechanism are improved.