The Internet of Things (IoT) refers to a network concept that extends its clients to any item for information exchange and communication. Blockchain is a new application paradigm of distributed data storage, point-to-point transmission, consensus mechanism, asymmetric encryption, intelligent contract and other computer technologies. The combination of block chains and the IoT has led to the further development of many new technologies Blockchain technology for IoT has been a hot topic in academia and industry. This paper mainly summarizes the main challenges faced by IoT, the technical characteristics of blockchain, and the advantages and challenges of applying blockchain technology in IoT, and related work of block chain for IoT.