Heat wave (HW) is a type of extreme climate that has been occurring frequently in recent years. It affects the vegetation health of ecosystem in the short term and has the long-term negative influence on ecosystem carbon flux, but the intensity of its influence tends to vary depending on the type of ecosystem. The meadow grassland of the Inner Mongolia Plateau is a high-latitude semi-arid ecologically fragile area, which is significantly affected by climate change and is suffering from frequent heat wave. Therefore, this study conducted a two-year in-situ simulated heat wave control experiment in Hulunbuir meadow grassland of theInner Mongolia, focusing on the influence of heat wave on key processes of ecosystem's carbon cycle and the regulatory mechanism, and studying the interaction between human activities (mowing) and extreme climate (heat wave) on meadow grassland carbon flux. The results showed that heat wave treatment significantly reduced the soil water content of ecosystem, as well as net carbon exchange (NEE), ecosystem respiration (Re) and gross ecosystem productivity (GEP) of meadow grassland by 31%, 1% and 14%, respectively. However, the mowing treatment can effectively reduce the negative influence of heat wave, which is reflected in that time required for grassland recovery after the heat wave is shortened by 1/3. Meanwhile, water supply after heat wave can alleviate the legacy effect of heat wave on ecosystem carbon flux and shorten the recovery time of ecosystem.