Abstract: Radioisotope thermoelectric generator which uses Seebeck effect converting heat energy generated by the decay of radioisotopes into electrical energy is widely used in the space. The most widely used radioisotope thermoelectric generator is the ²³⁸PuO₂ radioisotope thermoelectric generator. It has many advantages such as long life, high reliability, etc. But the manufacturing technique of ²³⁸PuO₂ is very complex and the product is rare. There is not enough ²³⁸PuO₂ for the radioisotope thermoelectric generator. It is necessary to seek for the substitution for the ²³⁸PuO₂. The radioisotope ²⁴¹Am has many advantages to use for the radioisotope thermoelectric generator. The feasibility of ²⁴¹AmO₂ used in the radioisotope thermoelectric generator is analyzed. An ²⁴¹AmO₂-radioisotope thermoelectric generator based on the GPHS is designed. The finite elements software ANSYS is used to calculate the electrical output and the temperature distribution of the RTG in the temperature of the day and night of the moon surface. The electrical output of the two working states is nearly 2 watt, and the converting efficiency is about 3.5%. The calculation result shows that the ²⁴¹AmO₂ radioisotope thermoelectric generator is well adapted to the moon surface environment. The converting efficiency is slightly small than that of the European Space Agency, but is equal to that of the Korea Atomic Energy Research Institute. The analysis result shows that ²⁴¹AmO₂ can be used in the radioisotope thermoelectric generator.