We propose a co-coaxial coupling structure to realize power transmission in double-layer or multilayer rectangular SIWs at any direction. The proposed structure is formed a coaxial structure by adding metallic via and etching circular ring slot on the coupling section of each SIW layer. The shared coaxial coupling structure can support TEM mode for power transmission between different SIW layers. We take double-layer SIWs as an example and simulate its S-parameters from top layer to bottom layer when wave propagation directions (Delta theta) are designed at 0 degrees (parallel), 90 degrees and 135 degrees with a fixed matching network. The simulated results show that the S-11 is below -10 dB from 7.6 GHz to 10.3 GHz; S-21 is within -1.1 dB at 0 degrees and 90 degrees, and within -1.3 dB at 135 degrees in the operating frequency band.