Abstract: The design of communication protocol has become an important support for the communication between devices and the Internet, which covers all aspects of the entire Internet of Things system. Aiming at the security problem that the key data in the traditional Internet of Things protocol is forged or tampered with, an improved message queue telemetry transmission (MQTT) protocol is designed to ensure the security of the transmitted data by using blockchain technology in the process of data transmission. This ensures that the data stored in the broker is not maliciously tampered with. Simulation experiments show that this scheme has many characteristics, such as high efficiency, light weight and easy implementation, and has a remarkable effect in data security protection of the Internet of Things.