The new generation of smart grids has greatly improved the security and reliability of power grids, which relies on smart meters to send data every 15 minutes. However, this may expose the privacy of users and also requires a huge computation cost. As a result, data aggregation technology is introduced. Most of the existing aggregation schemes are time-consuming and the system cannot run normally when its meter fails. In response to the above problems, this paper proposes an efficient data aggregation scheme with fault tolerance in smart grids. Specifically, it uses the improved symmetric homomorphic encryption technology to be lightweight. It can resist collusion attacks while supporting fault tolerance. The security requirements analysis shows that the scheme is secure, and the performance evaluation reflects the efficiency of the scheme, which fits the smart meters with limited resources.