Abstract: A direct coupled finite element model was established based on experimental research, considering the influence of ultrasonic vibration on the yield strength and electrical contact resistance of 6061 aluminum alloy and TC4 titanium alloy during ultrasonic assisted resistance spot welding process. The evolution process of temperature and stress fields in ultrasonic assisted resistance spot welding based on thermal, electrical, and force coupling analysis. Simulation analysis shows that TC4 is not melted at the welding interface, and the joint is formed by the spreading and wetting of molten 6061 aluminum alloy on the surface of TC4 titanium alloy; The required heat during the welding process mainly comes from the Al-Ti interface, and the heat generation distribution inside the AA6061-TC4 plate is uneven. The temperature of TC4 is significantly higher than AA6061, and the high-temperature zone inside the AA6061 plate is distributed near the TC4 contact surface; The residual stress of welding at the joint is concentrated in a circular pattern along the edge of the heat affected zone of the titanium alloy.It shows that the morphology and size of the fusion nucleus are basically consistent with the numerical simulation results through the comparison with the metallographic test results, this model can effectively restore the temperature field and stress field of the ultrasonic assisted resistance spot welding process of AA6061-TC4 dissimilar alloy.