Abstract: Taking Ag coated graphene nanosheets (Ag-GNSs) as the reinforcement, new composite lead-free solders Sn-3.0Ag-0.5Cu- (Ag-GNSs) were prepared. The solder joints were prepared on the Cu matrix, and the isothermal aging treatment at 150 ℃for different time was carried out. The effects of different content of Ag-GNSs on the wettability of the lead-free solder Sn-3.0Ag-0.5Cu and characteristic of intermetallic compound (IMC) at the interface between Cu matrix and solder were studied. The results show that appropriate amount of Ag-GNSs can significantly improve the wettability of the solder, the wettability is best when the Ag-GNSs content reaches 0.05wt%, and the wetting angle is reduced by 54.43% compared with that of Sn-3.0Ag-0.5Cu solder. The IMC layer becomes thicker with the extension of the isothermal aging time, and its growth behavior is controlled by diffusion. The addition of Ag-GNSs can inhibit the growth of the IMC layer. The diffusion coefficient reaches the minimum value of 2.356×10^-18 m²/s when the Ag-GNSs content is 0.05wt%. The optimal addition amount of Ag-GNSs is 0.05wt % in the range of 0-0.2wt%.