Abstract: Forest carbon sink, an important factor in maintaining the ecological balance of the earth and coping with climate change, plays a key role in the global carbon cycle. It absorbs large amounts of carbon dioxide and stores carbon element, helping mitigate climate change. Additionally, forest carbon sink provides essential ecological services, such as biodiversity conservation, water resource regulation, and soil conservation. Therefore, the estimation of forest carbon sink is critical. Based on solar-induced chlorophyll fluorescence (SIF) and using the gross primary productivity (GPP) as an intermediate variable, this study estimated forest carbon sink in the forest region of Northeast China during the vegetation growth period (i.e., from June to September) between 2011 and 2020. The results reveal a strong spatial correlation between forest carbon sink and SIF in this region. The similar distributions of SIF values and carbon sink in the forest region of Northeast China indicate that the Changbai Mountains and the Da Hinggan Mountains had high and low carbon sink capacities, respectively. Over the vegetation growth period from June to September, the carbon sink capacity in the region showed a gradual upward trend initially, followed by a gradual downward trend. Overall, it is highly feasible to estimate carbon sink using SIF in the forest region of Northeast China.