Seasonal influenza remains a major global public health concern, causing substantial morbidity, mortality, and economic burden each year. China lacks age-stratified national estimates to inform vaccine policy and resource allocation, leaving an important evidence gap. Using a micro-costing approach, we calculated costs for each age group and then summed them from a societal perspective. The analysis was based on a real-world dataset of 12,784 laboratory-confirmed influenza cases. We estimated direct medical costs, direct non-medical costs, and productivity losses for both patients and caregivers. Deterministic sensitivity analysis (DSA) and probabilistic sensitivity analysis (PSA) were conducted to assess model uncertainty. The annual economic burden of seasonal influenza in China was estimated at 8.82 billion USD (95% CI: 7.24-10.80 billion USD). Direct medical costs accounted for 1.84 billion USD, direct non-medical costs for 0.43 billion USD, and indirect costs for 6.55 billion USD. Under the human capital approach, indirect mortality costs were estimated at 3.79 billion USD. Applying the friction cost method reduced this estimate to approximately 0.27 billion USD. Children younger than 5 y contributed the most to outpatient costs, whereas adults aged 60 y and older accounted for the largest share of inpatient costs. These findings provide robust economic evidence to support the expansion of publicly funded influenza vaccination programs. High-burden groups, particularly children younger than 5 y and adults aged 60 y and older, should be prioritized to reduce the health and socioeconomic impact of influenza.