Abstract: The present invention relates to a joining system for fast assembly structures of variable size, with which different size spaces are covered, the structures of the present invention can be two-dimensional or three-dimensional; these structure magnitudes vary in a very wide range. The joining system for structures of the present invention is essentially integrated by: a tubular element in which a bushing penetrates; a spherical head screw and a node where the screw is screwed. The spherical head when coupling the bushing makes possible a more functional structure assembly and the degree of freedom the system has during its assembly stage increase considerably due to the angles in which the tubular element can be placed with respect to the node are very wide, the aforesaid allows the structure assembly in a very diverse size range.