Meadow ecosystems serve as significant carbon sinks, playing a crucial role in the global carbon cycle. Precise simulation of carbon fluxes in regional-scale meadow ecosystems can provide a theoretical basis for understanding the feedback mechanisms of meadow carbon cycling to global changes. Ecological process models are essential for analyzing and predicting regional carbon balance budget. This study focused on the alpine meadow ecosystem in Gannan Prefecture and utilized the parameter-optimized Biome-BGC model to simulate the gross primary productivity (GPP) and net ecosystem productivity (NEP) from 1979 to 2018, characterizing the spatiotemporal distribution characteristics of carbon budget in this region. With the benchmark of 40 years of observed meteorological data and considering three Shared Socio-economic Pathways (SSPs) from the Coupled Model Intercomparison Project phase 6 (CMIP6), scenario simulations of meadow carbon balance budget in Gannan Prefecture from 2019 to 2100 were conducted. The results indicated that: the parameter-optimized Biome-BGC model performed well in simulating GPP and NEP of alpine grasslands in Gannan Prefecture, with a better performance in GPP simulation compared to NEP; (2) Alpine meadows in Gannan Prefecture behaved as a carbon sink throughout the study period, with GPP and NEP fluctuating between 600 g C m^-2 a^-1 and 1100 g C m^-2 a^-1, and between 150 g C m^-2 a^-1 and 300 g C m^-2 a^-1, respectively. GPP showed a significant increase, while NEP exhibited a fluctuating upward trend. Under future warmer and wetter scenarios, the carbon balance of alpine grasslands fluctuates greatly annually, with a trajectory that is first rising and then downward, with a very tiny NEP around 2060,and an average yearly increase of roughly 2.02 g C m^-2 a^-1, the carbon balance influenced jointly by temperature, precipitation and atmospheric CO₂ concentration in this region; (3) At the seasonal scale, the winter and spring seasons act as carbon sources, while the summer and autumn seasons act as carbon sinks, with carbon sequestration during the vegetation growth season enhanced. both GPP and NEP exhibit a reverse "U"-shaped trend throughout the year, with July and August serving as the peaks., low temperatures and ongoing warming have an inhibitory effect on carbon sequestration, while the amount of precipitation during the growing season is positively correlated with vegetation productivity; (4) Significant regional variations may be seen in the spatial distribution of carbon sinks and sources throughout time, with the development rate of carbon sinks generally decreasing from the southwest to the northeast.