At present, the centralized architecture for the Internet of Things (IoT) data management faces the risks of data leakage, single-point failure, and vulnerability to malicious attacks. Recently, many researchers and security analysts are focusing on the blockchain technology to solve the security and privacy issues of the IoT data management. However, current blockchain technologies are unable to meet the highly concurrent IoT data transactions and the fast expansion of IoT devices due to the decentralized architecture. Moreover, there is a lack of useful solutions for effective data sharing between public and private networks, and networks with different services (e.g., smart grid and intelligent transportation). In this paper, we propose a decentralized data access model for IoT data storage and sharing based on the FISCO-BCOS blockchain. In the model, we divide the IoT devices that handle different services into different set-chains. These set-chains share data with each other through an elaborate access control model. Experimental results show that the proposed model fits the characteristics of the IoT data management, guaranteeing the privacy and security requirements with better scalability. Our model can be used as a solution for smart cities.