Abstract: Achieving highly-efficient and clean utilization of coal has long been a primary concern in coal-fired power generation. Continuously improving power generation efficiency and reducing carbon emissions are paramount to the green-oriented and low-carbon transition. As an emerging power cycle technology, supercritical carbon dioxide （Sc-CO₂） power generation offers higher theoretical efficiency than conventional steam cycles and is expected to play a crucial role in enhancing future coal-fired unit efficiency and optimizing thermal systems. Compared to conventional steam boilers, Sc-CO₂ boilers exhibit a significant lack of engineering design experience. The validation of whether flue gas achieves efficient heat transfer across the entire temperature range and whether the working fluid attains the targeted thermodynamic parameters under a given design scheme has emerged as a pivotal research challenge for technological breakthroughs in the field of Sc-CO₂ boiler engineering. Therefore, establishing a complete Sc-CO₂ boiler thermal calculation system to obtain the temperature distributions of flue gas and working fluid at each heating surface is particularly important. Based on the domestically developed world's first 50 MW, 29.2 MPa/602 ℃/602 ℃ Sc-CO₂ boiler with a box-type configuration, a Sc-CO₂ boiler thermal calculation model is established. A thermal calculation platform for supercritical carbon dioxide has been developed using Fortran 90 and Python 3.11, enabling thermal calculations to obtain flue gas and CO₂ temperature distributions at each heating surface inlet and outlet. Based on the thermodynamic performance analysis, the current design successfully enables the superheated and reheated CO₂ to achieve the targeted thermodynamic parameters, and the flue gas duct arrangement is considered sound. However, an issue of excessive temperature differential between the inlet and outlet of the economizer has been identified. A comparative analysis of the design characteristics between the Sc-CO₂ boiler and conventional steam boilers is also provided.