In this article，theoretical calculation and experimental measurement of four and five fiber interfering field are investigated by using multi-fiber holographic interferometry. The effect of the central beam on the interfering field is explored，and the results show that the central beam only affects the interfering contrast without affecting the lattice structure. At the same time，by comparing the theoretical and experimental results，a good agreement is obtained. Furthermore，gradient photonic crystal (GPC) structures are designed for four fiber interferometry. The beam splitting and focusing effect is analyzed for GPC structures. This provides theoretical and experimental basis for the fabrication of good beam splitter and a focusing lens.