Data aggregation is a key technology in smart grid communication for collecting the most critical data in an energy-efficient manner. However, with the large-scale deployment of smart meters, this undoubtedly brings many privacy concerns to users, such as sensing their lifestyle habits. Therefore, in this paper, we propose an efficient and privacy-preserving data aggregation (EPPDA) for IoT-enabled smart grid based on smart contracts. Firstly, we propose a four-layer architecture of blockchain-based smart grid communication to support data aggregation. At the collection layer in the architecture, the underlying Boneh-Goh-Nissim system is improved to make it more suitable for grid privacy protection scenarios. In the platform layer of the architecture, the tamper-proof feature of blockchain is utilized for efficient storage and query of aggregated data. The performance analysis results indicate that the proposed EPPDA can meet several privacy characteristics of smart grid systems. Finally, experimental data shows that the proposed EPPDA reduces the computation and communication costs and improves the efficiency of the whole scheme.