In a method for statistical analysis of aggregate encrypted data with key-leakage resilience for smart grids, every user area is managed by a fog node which plays the role of data aggregation gateway and data relay. All the users' electricity consumption data sent by smart meters in the same user area are firstly aggregated by the fog node to generate a fog-level aggregate ciphertext. Then the fog node further generates a digital signature for the fog-level aggregate ciphertext and sends these data to a cloud server for long-time storage. The cloud server stores all the aggregate ciphertexts and digital signatures received from different user areas in its database, and provides data query and statistical analysis services for the control center of smart grids. On the premise of without violating users' privacy, the cloud server could provide enough information for the control center, enabling it to compute the sum, arithmetic mean and variance of all users' data in specified areas in a privacy-preserving way.