With the recent development of mobile communication technology and the popularization of smart devices， the computation-intensive tasks of the terminal devices can be offloaded to edge servers to solve the problem of insufficient resources. However， the distributed nature of computation offloading technology exposes terminal devices and edge servers to security risks. And， blockchain technology can provide a safe environment transaction for the computation offloading system. The combination of the above two technologies can solve the insufficient resource and the security problems in internet of things. Therefore， the research results of applications combining computation offloading with blockchain technologies in internet of things were surveyed. Firstly， the application scenarios and system functions in the combination of computation offloading and blockchain technologies were analyzed. Then， the main problems solved by blockchain technology and the key techniques used in this technology were summarized in the computation offloading system. The formulation methods， optimization objectives and optimization algorithms of computation offloading strategies in the blockchain system were classified. Finally， the problems in the combination were provided， and the future directions of development in this area were prospected.