The wetting behavior of liquid tin (Sn) solder on copper (Cu) substrate at 250 ℃ was investigated by the wetting balance method under the action of direct current (DC). The curves of wetting balance were measured and the morphology of the intermetallic compound (IMC) precipitated at the interface were observed. Results show that DC has a significant effect on the wettability and IMC. As the current increases, the balance wetting force and the thickness of the IMC layer increase. The direction of the DC also has a certain effect on the balance wetting force and IMC layer. When the current is negative, the final balance wetting force and the thickness of the Cu₆Sn₅ layer are significantly higher than those in the positive current case, which is attributed to electromigration. The IMC precipitation at the interface provides a chemical driving force for the movement of the triple junction. The interaction of the interface atoms and the chemical reaction are enhanced by DC, thereby improving wettability. Meanwhile, the Marangoni convection caused by DC inside liquid Sn solder changes the structure of triple junction, which provides a physical driving force for the spread of the liquid Sn solder on the Cu substrate.