A joint structure, which allows a user to individually assemble and strengthens the stability of steel pipes. The joint structure mainly comprises of a fixture element, which can be slipped into a vertical steel pipe, a joint block, which connects two transversal steel pipes on the inner sides, and a fixture screw, which fastens a joint block and the vertical steel pipe to unite both of the transversal steel pipes and the vertical steel pipe. On the bottom of the vertical steel pipe and the fixture element, there are overlapped fixture screw holes. Both of the inner ends of the transversal steel pipes having clip holes. On the bottom of the extension panels located on the lateral sides of the joint block, there are inert blocks, which fit exactly with the clip holes. In the middle of the joint block, there is a piercing hole. By respectively inserting both of the insert blocks on the joint block into the clip holes on two transversal steel pipes, the extension panels on both sides of the joint block fit exactly the inner end of both the transversal steel pipes. Thus, fixture screw may pass the piercing hole on the joint block and join the fixture screw holes on the vertical steel pipe and the fixture element to firmly fasten the transversal steel pipes and the vertical steel pipes. As a result, the steel pipes can be easily and conveniently dismantled and assembled by consumers to achieve the effect of reducing material volume for delivery.