Using land use data from 2010, 2015, and 2020, this study takes Huangping County, Guizhou Province—a national key ecological functional area—as an example. It couples the InVEST and PLUS-Markov models to analyze the characteristics of construction land expansion in Huangping County and its impact on the regional carbon stock. The study then predicts carbon stock changes in 2030 under three development scenarios (ecological protection, natural development, and economic construction), in line with the “14th Five-Year Plan”. The results show that from 2010 to 2020, the area of construction land in Huangping County increased by 1792.89 hm² (a growth rate of 33.65%), with urban, rural and industrial-mining land as the dominate types during the expansion. Construction land conversion caused a net carbon stock loss of 5.93×10⁴ t, primarily due to the conversion of forest land, farmland and grassland to construction land. Overall, the total carbon stock in Huangping County exhibited a growing trend from 2010 to 2020, increasing from 247.56×10⁵ t to 276.03×10⁵ t. Area with significant carbon stock growth, basically unchanged stock, and significant decline accounted for 69.28%, 6.27%, and 24.45% of the total area, respectively. By 2030, the projected carbon stocks under the ecological protection, natural development and economic construction scenarios will be 274.76×10⁵, 267.22×10⁵ and 266.76×10⁵ t, respectively. The study recommends implementing the scenario management mode of “ecological protection is the main focus, and economic construction is the supplement” from 2025 to 2030.