Abstract: In nuclear power plant wet scrubbers and chemical plant bubble columns, where radioactive decay and exothermic reactions occur respectively, the liquid phase may experience continuous and uniform volumetric heating and have an obvious influence on the evaporation process. The existing research has predominantly focused on bubble evaporation under non-continuous heat sources or boundary heating conditions, but the mechanisms of bubble phase change under the unique thermal boundary of continuous uniform volumetric heating are still scare. This study investigates the migration and distribution characteristics of water vapor within bubbles under conditions of continuous uniform liquid heating, with particular focus on the effects of decay heat power. For volumetric heating powers increased by equal increments, the difference between the non-heating condition and the lowest heating power case exhibits the most substantial changes in bubble velocity, evaporation rate, and water vapor concentration near the gas-liquid interface. Specifically, the application of continuous uniform heating leads to an increase in near-interface vapor concentration, accompanied by significant decreases in both bubble velocity and evaporation rate. When comparing cases with heating powers separated by subsequent increments of the same magnitude, the vapor concentration and bubble velocity continue to rise, while the evaporation rate continues to decline, with the magnitudes of these variations being considerably smaller than those observed between the non-heating and the lowest heating power cases. These findings enhance the understanding of bubble phase change under continuous uniform heating and provide a theoretical basis for thermal-hydraulic safety analysis and design optimization of relevant industrial equipment.