Welding residual stress is a critical factor contributing to the deformation of spacecraft cabin bodies during CNC machining. To mitigate such machining deformation, this paper conducts simulation and experimental studies on ultrasonic vibration-based stress regulation of electron beam welds in 5B70 aluminum alloy cabin bodies. This reveals the influence of the law of amplitude and treatment times on weld residual stress. A stress regulation process scheme for 45 mm thick plate butt welds is proposed: An ultrasonic amplitude of 30 μm, with two repeated treatments on the front side of the weld. After stress regulation, the peak values of transverse residual stress σ_x and longitudinal residual stress σ_y on the back surface of the weld are reduced by 33.94% and 67.05%, respectively. And the corresponding homogenization rates are 22.22% and 22.37%, respectively. Milling tests show that the machining deformation of the stress-regulated specimens in the Z-direction is reduced by 64.48%, which validating the efficacy of ultrasonic vibration-based regulation of welding residual stress in reducing cabin body machining deformation.