Narrow-band Internet of things （NB-IoT） is an emerging wireless communication technology in the field of Internet of things. Its standard core protocol was officially settled in June 2016. NB-IoT can provide a strong support to the connection of Internet of things in the future for its features such as an extensive coverage，supporting massive connection，low power consumption and low cost. At present，operators worldwide are accelerating the deployment in NB-IoT，while enterprises are actively promoting the technical practice of NB-IoT.