Abstract Accurate quantification of interannual variations in China’s fossil fuel CO2 (FFCO2) emissions is critical for climate policy evaluation. However, bottom‐up inventories exhibit growing discrepancies. Here, we estimate China’s 2015–2023 FFCO2 emissions using the Regional multi‐Air Pollutant Assimilation System, integrating in situ observations of co‐emitted NO2 and grid‐specific CO2‐to‐NOx ratios. National FFCO2 emissions averaged 11.5 ± 1.5 PgCO2 yr−1, with over 45% from North and East China. Emission intensity exhibited a southeast‐to‐northwest increasing gradient, aligning with economic development patterns. Interannually, emissions rose notably during 2015–2017, driven by North and Central China, then stabilized during 2018–2023 amid policy interventions and COVID‐19 disruptions, contrasting with the sustained growth reported in mainstream bottom‐up inventories. Total annual growth averaged 189.6 TgCO2 yr−1 (1.6%), while emission intensity fell 5.6% annually, with Southwest China experiencing a decline in both metrics. This observation‐constrained data set clarifies spatiotemporal dynamics and policy impacts, supporting targeted strategies for China’s carbon goals.