In this work, Sn-based active alloys were used to solder a Mo electrode and Al together, and the effect of active Al on the Mo/solder interface was studied with methods of first-principles calculation and experiments. The Mo(110)/ Sn(001) interface with bridge site was found to have the largest work of adhesion (W ad). The heat of segregation (DG seg) results reveal that Al atoms prefer to diffuse to the interface and form bonds with Mo, resulting in the Al-Mo intermetallic compound (IMC) layer. When two Al atoms appear at the interface, the value of W ad increases to 3.02 J/m 2 dramatically, which indicates that Al strengthens the Mo/Sn interface. Then pure Sn, Sn-9Zn, Sn-9Zn-2Al, and Sn-13.5Zn-10Al alloys were prepared to solder Mo and Al assisted by ultrasound. Pure Sn and Sn-Zn solders have weak bonding with Mo, and the joints fractured from the interface with very low strength. When the Sn-9Zn-2Al and Sn-13.5Zn-10Al solders were used, the active Al segregated to the interface and reacted with Mo. The interface was strengthened by the Al-Mo IMC layer. The joints fractured inside the solder layer, and the shear strength of joints using Sn-13.5Zn-10Al reached 35 MPa.