For deep space exploration, the performance of an alkali metal thermoelectric converter (AMTEC) can be improved by utilizing the thermoelectric generator (TEG) subsystem. In this work, a coupling system comprised of an AMTEC and a TEG is proposed, in which the waste heat produced by the AMTEC top cycle is used by the TEG bottom cycle cooled by a heat pipe radiator. A general mathematical model is built to analyze the output power and efficiency of each subsystem and the whole system. Finally, the effect of critical parameters on the output power and efficiency are evaluated, including the current density of AMTEC, dimensionless current i of TEG, geometrical structure, and operating environment. The results show that the combined AMTEC/TEG system is 4.35% and 15.39% higher than the efficiency and output power obtained when using the TEG subsystem to recycle the waste heat from the AMTEC condenser. The thermoelectric conversion performance of the AMTEC/TEG system is related to that of the AMTEC subsystem while less affected by the TEG subsystem. The present work could provide a new route for constructing long-distance nuclear space power stations, rovers, and lunar bases in extreme environments.