Abstract: ObjectiveTO INVESTIGATE THE DESTRUCTIVE EFFECTS OF DEBRIS FLOWS ON MASONRY STRUCTURES, MethodsTHE TIANBEIGOU DEBRIS FLOW IN HANYUAN COUNTY, SICHUAN PROVINCE, WAS SELECTED AS THE STUDY SUBJECT. FIRST, THE MASSFLOW NUMERICAL SIMULATION METHOD WAS EMPLOYED TO CONSTRUCT A SEDIMENT FLOW DYNAMICS MODEL. THIS MODEL DERIVED FLOW DEPTH AND VELOCITY FOR DIFFERENT RAINFALL RECURRENCE INTERVALS (10-YEAR, 20-YEAR, 50-YEAR, 100-YEAR) AND DELINEATED HAZARD ZONES WITHIN THE TIANBEIZI GULLY WATERSHED. SUBSEQUENTLY, CONSIDERING BOTH THE IMPACT AND BURIAL EFFECTS OF DEBRIS FLOWS ON STRUCTURES, A PRECISE VULNERABILITY MODEL APPLICABLE TO DOUBLE-LAYER MASONRY STRUCTURES WAS DEVELOPED. FINALLY, A QUANTITATIVE RISK ASSESSMENT METHOD COUPLING DEBRIS FLOW DYNAMICS WITH STRUCTURAL VULNERABILITY MODELING WAS ESTABLISHED. ResultsTHE RESEARCH FINDINGS INDICATE: (1) UNDER FOUR DIFFERENT RAINFALL RECURRENCE INTERVALS, THE MAXIMUM DEBRIS FLOW VELOCITIES WERE 9 M/S, 8 M/S, 6.5 M/S, AND 6 M/S, RESPECTIVELY, WITH MAXIMUM SEDIMENT DEPTHS OF 7.6 M, 7 M, 6.4 M, AND 6 M; (2) THE NUMBER OF BUILDINGS AFFECTED BY DEBRIS FLOWS INCREASED FROM 10 TO 19 AS RAINFALL RECURRENCE INTERVALS INCREASED FROM 10-YEAR TO 100-YEAR EVENTS; (3) COMPARING THE 10-YEAR AND 100-YEAR RAINFALL RECURRENCE PERIODS, THE TOTAL AREA OF THE RISK ZONE INCREASED FROM 8.62×10⁴ M2 TO 13.08×10⁴ M2, REPRESENTING A 51.71% INCREASE. ConclusionsTHESE FINDINGS PROVIDE THEORETICAL GUIDANCE AND SCIENTIFIC SUPPORT FOR DEBRIS FLOW DISASTER PREVENTION AND MITIGATION IN THE MOUNTAINOUS REGIONS OF SOUTHWEST CHINA.