The invention provides a prepress tightening device and a method for a carbon fiber composite core wire matching fitting. The prepress tightening device for the carbon fiber composite core wire matching fitting comprises a fixing frame, a stop plate and a driving piece, wherein at least one limiting plate is arranged on the fixing frame, and the limiting plate is provided with a limiting hole for enabling an outer cone seat to pass through; the stop plate is detachably connected with the fixing frame and is parallel with the limiting plate; a stop hole is arranged at the place, corresponding to the limiting hole, on the stop plate; the diameter of the stop hole is larger than the outer diameter of the small end of an inner cone clamp and is smaller than the outer diameter of the outer cone seat; and the driving piece is provided with a telescopic rod, the telescopic rod can be inserted to the outer cone seat to abut against the large-end surface of the inner cone clamp, the telescopic rod is stretched out to abut against the inner cone clamp, the inner surface of the inner cone clamp can be tightly attached to the outer peripheral surface of a mandrel, and the outer peripheral surface of the inner cone clamp can be tightly attached to the inner surface of the outer cone seat. According to the prepress tightening device and the method for the carbon fiber composite core wire matching fitting, the pre-tightening forces between the inner cone clamp and the outer cone seat and the mandrel in the case of operation at each time can be ensured to be consistent.