Ubiquitous Internet of Things (UIoT) is required a 3-D network that stretches from space to air to earth. It involves numerous network components, such as satellites, HAPs, UAVs, terrestrial cellular networks, data centers, terrestrial gateways, as well as sharing and openness among operators. Correspondingly, wireless spectrum sharing becomes essential to energy efficiency and, thus, has to be investigated for green UIoT. Meanwhile, both blockchain and sixth-generation mobile communication technology hybrid cloud are recently intriguing technologies, and the enormous potential of combining the two has grown in prominence. For the reason of dependability and security, these two technologies are proposed to apply to spectrum sharing among UIoT devices. Particularly the blockchain’s unique smart contract technology can well complete the spectrum sharing procedure, as verified by the numerical results from our simulation study.