Abstract: A sealed outer welding cover structure for sensors and pipelines at the bottom of the propellant tank of a launch vehicle to provide protective seal for the sealing surfaces between sensors & valve pipelines and tank bottom flange was proposed. In view of the risk of low capability of the tank bottom sensor to withstand the welding thermal effect of the outer welding cover, a thorough experiment was carried out. A heat dissipation plan for the welding process was developed. Process parameters such as welding time and heat disssipation time were determined. The proposed research may provide a technical support for the subsequent welding of the outer welding cover for sensors on the launch vehicle.