Abstract: In order to study the impact of scale effect of rock sample on seepage characteristics of water and sand mixture in broken rock,the authors design a water and sand infiltration system and use CMT5305 electronic universal testing machine to conduct a test. According to the test results,a sieving model of broken rock is proved,and a relationship is presented to characterize the comprehensive influence of initial porosity and sieve layer thickness on the ability of filtering sand. When the initial porosity of broken rock are same,the increase of thickness of rock sample can increase the ability of filtering sand of broken rock and reduce the amount of sand inrush,thereby the risk of sand inrush disaster can be reduced. When the initial porosity of broken rock is greater,the impacts of thickness of rock sample on the amount of filtering sand are greater,while when the initial porosity of broken rock is relatively small,the impacts of thickness of rock sample on the amount of filtering sand are smaller. While the thickness of rock sample increases,the ability of filtering sand will not infinitely increase.