<p>An experimental prototype of the low-temperature radioisotope thermoelectric generator (RTG) was constructed based on Bi₂Te₃ thermoelectric (TE) materials suitable for low-temperature operation. Using radioisotope Am-241 as the heat source, the relationship between the load voltage and the output performance of the RTG prototype was experimentally measured. A comprehensive 3D finite element method (FEM) model of the low-temperature RTG, matching the dimensions of the experimental prototype, was developed by using COMSOL Multiphysics. The simulation results show good agreement with experimental data, confirming the validity of the FEM model. The heat transfer mechanisms and thermoelectric behaviors were thoroughly analyzed, and potential theoretical improvements and optimization strategies were proposed to support the feasibility of low-temperature RTGs in low-watt power supply applications. The impact of radioisotope decay on the output characteristics was investigated. Additionally, parametric analysis was conducted to study the effect of the thermal insulation, fin geometries, and emissivity properties of the RTG housing on system performance. Considering practical deep space scenarios, the influence of solar radiation on the temperature distribution and performance of the RTG was also evaluated. Future research aims to build RTGs with strong adaptability to diverse mission requirements and better output performance.</p>