Internet of things (IoT) technology has been a hot research direction in recent years. Low Power Wide Area Network (LPWAN) is an important part of IoT. It helps realize smart cities, guarantees logistics security, and food security. It has important applications in both industrial and agricultural fields. Ultra narrow band (UNB) are systems that have very high spectrum efficiency but with restricted communication rate. It has become a popular choice for LPWAN due to its high anti-interference ability and low energy consumption. Therefore, in recent years, many LPWANs based on UNB technology have been developed. This paper introduces UNB, LPWAN, and IOT technologies in detail, and explains how LPWAN and UNB are used in IoT technologies. Then three UNB-based LPWAN networks, Sigfox, Telensa, Weightless-N, are introduced. Finally, we will compare these three technologies in terms of system composition, performance and application to find out their advantages and disadvantages in different aspects.