Two dimensional materials have demonstrated attractive properties for physical and technological applications since the discovery of graphene. In contrast to graphene as zero gap semiconductor, 2D single layer crystalline phase of group V elements with a buckled honeycomb structure, such as arsenene, bismuthene and antimonene, were predicted to exhibit a broad range of band gap and high mobilities in optoelectronic applications. In present work, we derive the electronic structure of a heterostructure comprised of group V 2D monoelemental material and topological insulator. Proximity effects that occur in heterojunctions comprised of topological insulators and materials can provide an interesting platform to produce emerging quantum phenomena of Dirac fermions at the interfaces. Herein, we demonstrate a novel phenomenon termed the topological proximity effect, which occurs between a 2D material and a three-dimensional topological insulator. 2D monoelemental materials, such as bismuthene and antimonene, well prepared on 3D topological insulators. The surface morphology examined with scanning tunneling microscope (STM) revealed the formation of a large area of antimonene bismuthene with a buckled structure. A topological phase transition was observed in a heterostructure of 2D normal insulator and 3D topological insulator (NI/TI) with angle-resolved photoemission spectroscopy (ARPES) and confirmed by the density function calculation (DFT). On contrary to the heterostructure of 2D NI/3D TI, 2D metal/3D TI exhibits large Rashba splitting at the interface between metal and TI. Both findings demonstrate a promising way that the spin-texture can be tuned in either NI/TI or metal/TI structures. Our finding provides a potential system to fabricate future spintronic devices.