Abstract: High temperature gas-cooled reactor (HTR) is of a potential of using combined cycle to generate electricity due to high reactor core outlet temperature of 900-1000 ℃. In a typical combined cycle of HTR, a precooler was used to reduce the compressor inlet temperature and the compression work, while it also lowers the reactor core inlet temperature and hinders the further improvement of cycle efficiency. To improve cycle efficiency, the influence of precooler on efficiency of the combined cycle of HTR was analyzed theoretically. And a criterion was deduced to determine whether a combined cycle of HTR adopts a precooler based on the analysis. A simplified combined cycle system without precooler was proposed based on the criterion. The optimization results show that the efficiency of the simplified combined cycle is 1.4% higher than that of the typical combined cycle and 1.7% higher than that of the recuperative cycle with reactor core outlet temperature of 950℃. Compared with the recuperative cycle, the simplified combined cycle is more competitive in work conditions with high reactor core outlet temperature and low reactor core inlet temperature.