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With the large resources invested by many countries in the world, the networks of quantum communication have been developed. However, with the increase of communication distance, the losses on the communication line will greatly limit the distance of quantum communication. On the other hand, the no-cloning theorem that protects the security of quantum communication also restricts the application of classical repeater stations through amplifying the attenuated signal in quantum communication. To resolve this problem, the concept of quantum repeater (QR) protocol was proposed. The protocol uses the unique characteristics of quantum mechanics such as entanglement swapping (ES) to further distribute quantum correlations, entangle the nodes that have never interacted, and even resist losses caused by the transmission lines to achieve long-distance quantum communication. In this article, we discuss the difficulties encountered by quantum communications over long-distance transmissions and explain the solution: QR protocol. With the different architectures of QR protocol, their protocols can be divided into memory-based and all-optical types. We will introduce the physical principles of the two different types of QR and the process of the protocol. We also report on some recent progresses of QR. In addition, we also discuss the twin-fi eld quantum key distribution (TFQKD) scheme, recently proposed for long-distance quantum communication. We believe that this report will help the readers to understand the architecture of long-distance quantum communication and the technical challenges that it faces. [ABSTRACT FROM AUTHOR]