Fixed connection device of vertical tube and joint of folding bicycle

The utility model discloses a fixed connection device of a vertical tube and a joint of a folding bicycle. The fixed connection device comprises a front fork vertical tube, a lower joint and a compression bolt, wherein the lower joint sleeves the front end of the front fork vertical tube; the compression bolt is used for connecting the lower joint with the front fork vertical tube; the lower joint is a complete continuous annular component; an inner hole of the lower joint is a taper hole with a small upper part and a big lower part; a conical collet chuck with at least two deformation grooves in one wall body is matched with the taper hole; a sliding nut with an upper bulge loop and a lower bulge loop which are arranged on an excircle is in threaded connection with the compression bolt; the sliding nut is connected with an inner hole hook of the conical collet chuck by the lower bulge loop; a limit groove which is capable of preventing the sliding nut from sliding relative to the conical collet chuck is also