Abstract: Zhaizi rockfall collapsed many times in the history and a large number of residual dangerous rock masses seriously threaten the life and property safety of 420 villagers below the rockfall. It is urgent and necessary to carry out the corresponding risk assessment research. In this paper, the geological and geometric information of the collapse are obtained by UAV tilt photography, 3D scene modeling and ploywork point cloud data processing technology, and three dangerous rock masses on the slope were detected. The volume of dangerous rock mass was determined according to the combination relation of structural plane and the assumed section method. Based on the statistics of the historical rockfall, the collapse annual occurrence probability was derived from a MCF distribution of rockfall event. Based on the retention position of the historical rockfall, the probability of rockfall arrival was obtained by means of parameter inversion and random rockfall simulation analysis. Combined with the analysis of spatial and temporal distribution probability and vulnerability, the quantitative risk assessment(QRA) of this rockfall is carried out. The results show that no matter in sunny or rainy days, the risk values of blocks 1,2 and 3 are in the warning range. It is suggested to strengthen monitoring and take certain disaster prevention and mitigation measures. The assessment method and results can provide a reference for quantitative risk assessment of other rockfall research.