<p>Aluminum/magnesium alloys have increasingly important applications in the lightweight design and manufacturing of vehicles due to their excellent mechanical properties. The body and body panels of new energy vehicles contain numerous Al/Mg/Al three-layer plate spot welding structures. In this study, aiming at the common problem of difficult welding of heterogeneous metals, the spot welding connection of Al/Mg/Al three-layer plates was achieved by using ultrasonic welding technology. Meanwhile, a thermal-force coupling analysis model of the ultrasonic welding process was established and the accuracy of the model was verified. The research results show that with the increase of welding energy, the tensile shear strength of the joint first increases and then decreases. The failure modes of the joint are all interface failure, and the maximum tensile load reaches 704&#xa0;N. The interface bonding mechanism is mainly due to mechanical interlocking formed by plastic deformation, and no metallurgical reaction occurs. The distribution and evolution laws of the temperature field and stress field under different parameters were obtained through the numerical model, and the maximum temperature during the welding process can reach 550℃. The research results will provide new ideas and theoretical support for the study of heterogeneous metal three-layer plate spot welding structures.</p>