In Smart Grids(SG), measured user data in Smart Meter(SM) in residential area are sent to Control Center(CC) passing through a few intermediate nodes. Hence, privacy preserving of user data is one of the biggest challenges in smart grid researches because the habits and behaviors of users can be disclosed by data mining the User-Related Data(URD). A Privacy-Preserving Data Aggregation(PPDA) algorithm is proposed. In PPDA algorithm, the Group Location Privacy(GLP) approach is taken advantage to mask fine-grained user data generated by SMs, and Paillier encryption system is utilized to preserve the user data privacy. The proposed protocol does not need any secure channel. The security and performance analysis shows that the proposed approach is secure against eavesdropping attack and collusion, and its computational overhead is acceptable compared with that of the previous works.