Recently, the research group of Prof. Zeng-Bing Chen and Associate Prof. Hua-Lei Yin (National Laboratory of Solid State Microstructures and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University), cooperating with Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences and other institutes, proposed a four-phase measurement- device-independent type quantum key distribution (QKD) protocol and implemented a proof-of-principle experiment to prove the feasibility.