Abstract: Given the frequent occurrence of fall-back hazards in mountain tunnels and the limitations of existing risk assessment methods, this study proposes a new quantitative evaluation approach by integrating matter-element theory, block theory, and statistical rock mechanics. First, a block formation probability calculation method was developed based on the distribution law of structural plane trace lengths. Using this method, a probability classification system for block falls was established by combining the risk event probability classification standard with the characteristics of random blocks. Subsequently, block theory was applied to calculate key parameters of random blocks, including their position, volume, and safety factor. On this basis, a block loss calculation method was constructed using matter element theory, and a loss classification standard was developed according to risk-event loss grading criteria. By integrating the probability and loss calculations, a quantitative risk evaluation method for fall-block hazards in tunnels was formed. The method was applied to the risk assessment of falling blocks in the left tunnel of the Yanqian Tunnel on the Beijing-Taizhou Expressway. The results show that the calculated results are consistent with field observations, demonstrating both the advancement and practical applicability of the proposed method.