The invention discloses a simply-supported type wind tunnel testing device for resistance coefficient of a long and thin member. Force measuring sections with the same structure are symmetrically arranged at the left and the right of a test section of a building wind tunnel; force measuring balances are respectively fixed above two supports, clamping seats are respectively fixed above the force measuring balances, the two supports are fixed on a ground of the test section, and openings of the two clamping seats face a blowing direction. An arc-shaped rubber sheet is arranged at the bottom of aguide surface of an opening on a rear side surface of the two clamping seats, and size requirements of round rods at two ends of a test piece of the long and thin member are smaller than a diameter of the arc-shaped rubber sheet; the round rods at the two ends of the test piece are placed on the arc-shaped rubber sheet of the two clamping seats through the guide surface so as to form a simply-supported type force measuring system; and two two-dimensional flow isolation boxes are respectively covered on the respective force measuring section to form a two-dimensional flow effect, and resistance of the test piece is obtained through the force measuring balances at two sides, so that the resistance coefficient of the test piece is obtained. By the adoption of the simply-supported type wind tunnel testing device for the resistance coefficient of the long and thin member, the resistance coefficient of a long and thin rod piece is tested, defects of a traditional testing device are overcome, and a new way is provided for a wind tunnel force measurement test of the resistance coefficient of the long and thin member.