Abstract: The high temperature gas-cooled reactor (HTR) has high reactor outlet temperature of 900-1000℃ and high cycle efficiency when combined with energy conversion systems of regenerative cycle and combined cycle. However, the regenerative cycle requires a high regenerator effectiveness. In the combined cycle, the reactor inlet temperature is so low that it hinders the further improvement of cycle efficiency. To further improve cycle efficiency, a compound cycle of HTR was proposed. The effects of precooler and regenerator on the compound cycle efficiency were analyzed. The results show that when the reactor outlet temperature is 950 ℃ and the regenerator effectiveness is 0.95, the efficiency of the compound cycle without precooler reaches 54.2%. The efficiency difference between the compound cycles without precooler and with precooler drops from 1.7% with the increase of the regenerator effectiveness. The comparison of the regenerative, the combined and the compound cycles suggests that it is a more effective way to improve efficiency by increasing the total work production of the turbines than by decreasing the compression work of the compressor. When the reactor outlet temperature ranges from 900 ℃ to 1 200 ℃, the optimum efficiency of the compound cycle is 3.6%-4.0% higher than that of the regenerative cycle and 1.9%-2.7% higher than that of the combined cycle. When the limit of the reactor inlet temperature is higher than 500-550 ℃, the compound cycle has the highest efficiency.