An overview of quadrature-based quantum key distribution is provided. Beginning from the comparison between
single-photon schema and continuous variable schema, the article focuses on the classical and state-of-art
protocols. Protocols' main procedures and security analysis are introduced, which includes the methods under
individual attack and collective attack. Then recent development of unconditional security proof is introduced
including the optimality of Gaussian attack and de Finetti theorem. Introduction towards discrete modulated
schemas' security proof is also made. At last, the article discusses experimental realization of various protocols
and the main trend in this field.