Abstract: In this paper,the effects of thermal cycling on the microstructure,interfacial IMC morphology,thickness variation and tensile strength and tensile fracture morphology of Cu/Sn-58 Bi/Cu and Cu/Sn-58 Bi-0. 03 CNTs/Cu joints were studied. The results show that the Cu/Sn-58 Bi-0. 03 CNTs/Cu microstructure is relatively thinner under the same thermal cycling condition,and the thickness of the IMC layer increases with the increase of the thermal cycle number. With the increase of the thermal cycle,and the tendency of the CNTs particles to enhance the interface of the Sn-58 Bi composite solder joint interface is slower. The tensile fracture appearances of Cu/Sn-58 Bi/Cu solder joints and Sn-58 Bi-0. 03 CNTs/Cu solder joints after thermal cycling is mainly composed of dimples and a few cleaved surfaces. The fracture mechanism of Cu/Sn-58 Bi/Cu soldered joints changes from ductile fracture to tough-brittle mixed fracture mode,and the fracture mechanism of Sn-58 Bi-0. 03 CNTs/Cu soldered joint is ductile fracture.