An optical coupling apparatus, a fiber array unit, and a method for assembling the fiber array unit are provided. The optical coupling apparatus includes a coupling unit and a fiber array unit detachably connected to the coupling unit. The coupling unit includes a connecting base and a waveguide device disposed on the connecting base. The fiber array unit includes a ferrule body, a holding structure disposed in the ferrule body, and a plurality of optical fibers. The holding structure includes a front holding block and a guide holding block attached to the front holding block. The front holding block defines a plurality of front passages, the guide holding block defines a plurality of guide passages arranged in alignment with the front passages, and the optical fibers sequentially pass through the guide passages and front passages.