Abstract: How to simulate the core temperature distribution more accurately is one of the key issues in the safety analysis of the pebblebed high temperature gascooled reactor, especially in the study of veryhightemperature reactor operation. Due to the uncertainty of the pebble flow in the core, and the structural materials such as graphite blocks and carbon bricks assembled in bulk, the coolant flow paths in the reactor are complicated, which cause difficulties for accurate thermal hydraulic simulations, which can be further optimized. Based on the structure and flow path characteristics of HTR10, the heat transfer process was briefly analyzed, which illustrates the importance of accurately repartitioning the areas of structural components and coolant flow paths in the thermal hydraulic simulation to obtain a more accurate core temperature distribution. After the flow paths were analyzed in detail, the original thermal hydraulic model for HTR10 established in the THERMIX code was improved, simulating the bypass flow of core coolant more reasonably, and describing the core coolant flow and heat transfer process more accurately. Compared with the experimental results, the improved model significantly improves the simulating accuracy of the temperature distribution of the peripheral components of the pebble bed. The results also show that the maximum temperature of both the fuel and the graphite reflectors does not exceed the heat resistance limit of the material when the reactor is operating at full power and steady state under the rated design condition.