The wetting behavior of liquid Sn solder on Cu substrate at 250 °C was investigated by the wetting balance method under the influence of a direct current. The curves of wetting balance were measured and the morphology of the intermetallic compound (IMC) precipitated at the interface were observed. The direct current had a marked significant effect on the wettability and interface precipitation IMC. As the current increased, the balance wetting force and the thickness of the IMC layer increased. The direction of the direct current shown to have a certain effect on the balance wetting force and IMC layer. When the current was negative, the final balance wetting force and the thickness of the Cu₆Sn₅ layer were significantly higher than the current positive, which attributed to electromigration. The IMC of precipitation at the interface provided a chemical driving force for the movement of the triple junction. The interaction of the interface atoms and the chemical reaction enhanced with direct current, thereby promoted wettability. Meanwhile, the Marangoni convection caused by direct current inside liquid Sn solder changed the structure of triple junction, which provided a physical driving force for the spread of the liquid Sn solder on the Cu substrate.