Natural bitumen, as a rare unconventional resource characterized by non-toxicity and unique advantages in high-quality asphalt modification for road construction, necessitates systematic evaluation of its availability and reserve estimation to support exploration, reserve upgrading, and strategic resource security. This study proposes an integrated methodology for availability assessment and estimated reserves calculation of natural bitumen deposits. The approach evaluates the exploitable resource potential within specified periods based on geological occurrence conditions and current economic feasibility, thereby establishing scientifically grounded estimated reserves for strategic stockpiling. Through case analysis of China’s major natural bitumen deposits (Urho, Tianba, Datangpo, Jilue, and Aizhai), this research develops an availability evaluation system incorporating six critical indices: orebody depth, thickness, structural complexity, bitumen content, hydrogeological conditions, and geotechnical characteristics. Subsequently, the estimated economically recoverable reserves are derived by applying confidence coefficients and mine-specific recovery rates to categorized available resources.