Galileo mission detected the magnetic anomalies originated from Galilean moons. These anomalies are likely generated in the moons’ interiors, under the influence of a strong ambient Jovian field. Among various possible generation mechanisms of the anomalies, we focus on magneto-convection and dynamos in the interiors via numerical simulation. To mimic the electromagnetic environment of the moons, we introduce in our numerical model an external uniform magnetic field B ₀ with a fixed orientation but varying field strength. Our results show that a finite B ₀ can substantially alter the dynamo processes inside the core. When the ambient field strength B ₀ increases to approximately 40% of the field generated by the pure dynamo action, the convective state in the core changes significantly: the convective flow decreases by 80% in magnitude, but the differential rotation becomes stronger in much of the fluid layer, leading to a stronger field generated in the core. The field morphologies inside the core tend to align with the ambient field, while the flow patterns show the symmetry-breaking effect under the influence of B ₀. Furthermore, the generated field tends to be temporally more stable.