Given independent and flexible power supply requirements of space apparatus, miniaturized radioisotope thermoelectric generators are currently playing an increasing role in space power systems. This study creatively proposes a miniaturized integrated-design radioisotope thermoelectric generator based on concentric filament architecture and is the first to formulate a practical battery entity. When heat source temperature is 398.15 K, the maximum open-circuit voltage of 418.82 mV and the maximum output power of 150.95 μW are obtained. The COMSOL is used to simulate precisely the thermoelectric conversion process and optimize the structural size of the radioisotope thermoelectric generator. The optimal results are obtained when the ratio of N- to P-type circle radius and the thermoelectric filament's length are 0.1 and 20 mm, respectively. In this case, the battery obtains the maximum output power of 423.50 μW and open-circuit voltage of 605.84 mV when heat source temperature is 398.15 K. When the thermoelectric filament's curvature is 170°, the electrical density value increases more remarkably than that of 0°. Its effective open-circuit voltage density and output power density are 73.79 mV cm−3 and 53.76 μW cm−3, respectively. The optimized miniaturized radioisotope thermoelectric generator is able to provide power support for space microelectronic devices.