Abstract: The effect of Ni-CNTs content on the microstructure and shear properties of In-Sn-50Ag composite solder joints was studied. The results show that the addition of Ni-CNTs inhibits the growth of IMC（intermetallic compound） at interfaces, reduces the thickness of IMC layer, and the shape changes from loose to dense. The Ni-CNTs particles disperse in the in situ reaction zone and refine the Ag₃In structure. The shear strength increases first and then decreases with the increase of Ni-CNTs content. When the content of Ni-CNTs is 0.07wt%, the shear strength reaches the peak value of 41.5 MPa due to the fine grain strengthening and second phase strengthening. When the content of Ni-CNTs continues to increase, the agglomeration phenomenon increases due to the entanglement of Ni-CNTs in the in-situ reaction zone, and it is easy to produce stress concentration and crack around the agglomerated Ni-CNTs, which leads to the rapid decrease of the shear strength of the solder joint. Considering the microstructure and shear strength of the solder joint, it is determined that the optimal content of Ni-CNTs in In-Sn-50Ag composite solder is 0.07wt %.