The concept of coaxial di-nondiffracting beam is proposed. If two nondiffracting beams with small difference of convergence angle and common axis exist at same time, they will interference with each other to form a light field structure that varies periodically along the propagation direction. It is a new kind of space distribution of light beam. The cross-section of this beam is still rings fringe pattern with common center that can be used for precision alignment. However in different longitudinal position, the intensity distribution of these rings is different and varies periodically. The periodicity of the coaxial di-nondiffracting beam can be used for the positioning along the propagation direction. It is shown that the annular di-slit, axicon consisting of two conic surface and sine phase ring grating are capable of generating coaxial di-nondiffracting beam in theory and experiments. The diffraction pattern characteristics of coaxial di-nondiffracting beam along both transverse direction and longitudinal direction are analyzed. The experimental result fits to theoretical prediction basically.