Abstract: Addressing the challenges associated with controlling the weld throat size and the propensity for root crack formation in filler wire tube-to-tubesheet seal welding joints made of Incoloy 800H for nuclear power applications, this study implemented an integrated transverse motor module on the welding head. This integration enables oscillatory welding and variable-diameter rotary motion capabilities. Leveraging these functions, dimensional compensation for the varying weld bead profiles across different regions of the seal weld was achieved by adjusting key welding parameters (including oscillation dwell time, variable-diameter rotation, wire feed rate, welding current, and arc voltage). This approach allows for precise control over the morphology and dimensions of distinct zones within individual weld passes and across successive passes. Consequently, it effectively enhances crack resistance at the root gap while simultaneously ensuring an adequate weld throat size. The findings presented in this research provide significant guidance for mitigating root cracking and controlling weld throat size quality in nickel-base alloy tube-to-tubesheet seal welding.