Abstract: An adjustable bicycle stem structure comprising a horizontal tube and a longitudinal tube, one end of the longitudinal tube is provided with a rotatable shuttle-shaped threaded tube, and the corresponding end of the horizontal tube is provided with a push member. The external edge of the push member is provided with a row of toothed slots, which are distributed in the shape of a recessed arc. The toothed slots are made to mesh with the protruded threads of the threaded tube. When the shuttle-shaped threaded tube is rotating, it drives the push member to displace up and down following the threads on the threaded tube, allowing the horizontal tube to be adjusted up and down.