Abstract The Internet of Things (IoT), especially the industrial IoT (IIoT), has rapidly developed and is receiving a lot of attention in academic areas and industry, but IoT privacy risks and security vulnerabilities are emerging from lack of fundamental security technology. The blockchain technique, due to its decentralization and information disclosure, was proposed as a decentralized and distributed approach to guarantee security requirements and motivate the development of the IoT and IIoT. In this paper, we first introduce the basic structure and main features of blockchain and summarize the security requirements to develop IoT and Industry 4.0. Then, we explore how blockchain can be applied to the IoT for Industry 4.0 using its security tools and technology. We describe the most relevant blockchain-based IoT applications to promote the functions and advantages of the blockchain technique on IoT and IIoT platforms. Finally, some recommendations are proposed to guide future blockchain researchers and developers.