Efficient qubit extension is a fundamental problem that needs to be solved to obtain quantum speedup advantage for quantum computing. Due to its high feasibility and flexibility, distributed quantum computing (DQC) has become one of the key techniques for solving the qubit extension problem. According to different inter-chip communication modes, DQC can be divided into two types, teleportation-based and circuit-cutting-based DQC. The former mainly plays for the fault-tolerant quantum computing, while the latter is considered to effectively enhance the computing power of quantum computers in the noisy intermediate scale quantum (NISQ) era. In the long run, as one of the main applications of quantum network, DQC can efficiently harness the huge number of quantum computers connected to quantum networks to solve non-trivial problems. First, the origin and types of DQC are introduced. Then, the fundamentals and development of the two types of DQC, as well as widely studied application algorithms and compiling optimization methods, are provided.