The Internet of Things (IoT) brings people increasingly more convenience nowadays. However, due to the simple structure of most IoT devices and the limited budget when designing and building IoT systems, there are often security vulnerabilities in IoT systems. In addition, the accelerated growth of IoT devices and the data they generate also puts greater pressure on traditional centralised computing centers. Due to its openness, transparency, secure communication, and decentralisation, blockchain technology may solve these problems. This paper mainly studies the research trends of blockchain, IoT, and their integrated systems in recent years and puts forward issues worthy of attention in future development. This paper aims to help beginners get started with blockchain and IoT by providing an overview of blockchain, IoT, and their integration through reviewing and analysing literature. It recommends focusing on chain-chain communication security, new information compression and extraction methods, multi-dimensional evaluation of blockchain IoT systems, information security mechanisms against quantum computers in blockchain IoT integrated systems, and so on.