To realize the ultimate vision of Internet of Things (IoT), only depending on terrestrial network is far from enough. As a supplement and extension of terrestrial network, satellite network can offer powerful support to realize the depth and breadth of the coverage. However, existing satellite networks are usually designed for particular purposes. Moreover, traditional satellite networks and terrestrial networks are developed and operated separately, consequently they cannot meet the need of network flexibility required by IoT. In this paper, a space-terrestrial architecture is conceived for constructing a space-terrestrial based IoT (ST-IoT) system. Additionally, a reliable identification procedure, an integrated access and communication procedure, as well as a clustering cooperative transmission strategy are also presented.