In order to find the entry point of the applications of current quantum technologies in practical systems

this paper studies and analyzes the main technologies for current quantum communications and specially makes a theorectical analysis of the development and maturity of Quantum Key Distribution（QKD）-related protocols.Considering the constraints of the existing quantum device technologies

it concludes that the decoy state-based BB84protocol is the most mature QKD protocol and that quantum secure direct communication

quantum teleportation and other technologies are the the direction of quantum communication development.