Abstract: Check dams play an important role in the Loess Plateau region in stopping mud and stagnant floods,and silting up the land to make fields.Compared with earth and stone dams,check dams have lower flood control design standards,and in recent years,under the influence of extreme climate,sudden heavy rainfall has caused frequent cases of silt dam failure,which has brought great challenges to safety and management.In this paper,relying on the Wangmaogou silt dam in northern Shaanxi Province,different dosages of polyacrylamide are added,and the soil triaxial test,electron microscope test,and flume erosion test are conducted to reveal the mechanism of modified compacted loess based on the macroscopic and microscopic,and to improve the outburst characteristics of the silt dam.The results show that:polyacrylamide can improve the compressive strength of loess,strength increases with the increase of the dosage,in 300kPa perimeter pressure.0.25% dosage of PAM modified loess compressive strength than the compaction of loess increased by 199.6%;polyacrylamide will be dispersed soil bonded to form a larger agglomerate,reducing the number of pore space and the area of loess,0.25% dosage PAM modified loess porosity is only 1.0%,the pore size is only 1.0%,the pore size of loess is only 1.0%.Porosity of loess is only 1.79%,a reduction of 11.66%,enhancing the shear stress of soil scouring;polyacrylamide-modified compacted loess can significantly improve the degree of silt dam failure,prolonging the dam’s collapse time,0.25% PAM doping silt dam can be diffuse in 1 hour without loss,the peak of the failure flow rate of 708.3cm³/s,the dam body is basically intact,there is no obvious soil body The study provides important technical support for the construction of check dams and flood control.