[Objective] This study aimed to predict and evaluate debris flow disasters accompanied by material composition in construction waste sites to diverse mixed ratios of different spoils under heavy rainfall conditions and reveal the chain evolution mechanism and spatiotemporal distribution of the disaster chain in construction waste sites in mountainous areas under extreme rainfall conditions. These results provide a scientific basis for the prevention and control of soil erosion in mountainous regions. [Methods] Five cases （denoted as cases 1—5） comprising five different spoil compositions of miscellaneous fill， silt， and ceramic waste were designed to analyze and simulate debris flows accompanied by typical construction waste sites. Cases 1—5 involved single-material stacking or mixed stacking with different spoil composition proportions. The stability of the dam and slopes formed by the spoil， together with the characteristics of the debris flow after a dam break in the spoil ground， were systematically analyzed. A coupling dynamic model for landslides and debris flows was established using Massflow software. A hazard zonation evaluation of debris flows was performed based on the simulation results provided by the model. The sensitivity of the debris flow characteristics to the key model parameters impacted by the mixing ratios was investigated. [Results] ①The safety factors for the dam were 1.049， 1.002， and 1.034 when extreme rainfall occurred and building spoil ground was fully filled. The values for the filled materials were 1.172， 0.826， and 0.959， respectively. This indicates that extreme rainfall events triggers dam breaks， inducing instability in the filled material behind the dam， leading to debris flow along the downstream channel. ② The numerical simulation results showed that the maximum velocities of the debris flow in cases 1—3 were 21.04， 25.36， and 18.73 m/s，respectively. The maximum mud depths of the debris flows were 19.2， 8.2 and 12.7 m respectively. The farthest accumulation distances of the debris flows in cases 1—3 were 356.0， 674.8， and 545.4 m respectively. The areas of the high-hazard zones of debris flows in cases 1—3 were 36 068.1， 77 254.9， and 82 887.0 m2 respectively. ③ A joint analysis of the simulation results of cases 1—5 and ranking of factors （i.e.， internal friction angle > excess pore water pressure coefficient > unit weight） revealed that the internal friction angle and excess pore water pressure coefficient， which were affected by the mixing ratio， were the main controlling parameters for the debris flow characteristics. [Conclusion] Under the conditions of a full reservoir and extreme rainfall， construction waste sites in mountainous areas are associated with a high probability of causing a disaster chain of dam breaks， construction waste site destabilization， and debris flows， posing a serious threat to the safety of downstream residential areas and industrial facilities. The use of a reasonable proportion of materials in a mixed landfill scheme can effectively enhance the overall stability of construction waste sites and significantly reduce the area of high-hazard debris flow zones. A scientifically mixed landfill scheme can effectively control the influence of debris flow.