Abstract: Based on the unstable case of a highway slag dumping site,the slope stability of slag dumping project at different stages is systematically evaluated and analyzed to determine its disaster mechanism. Different reinforcement design schemes were compared to choose an optimal one. Using methods of investigation and monitoring,the treatment effect and surrounding engineering influence of the abandoned dreg sit are comprehensively evaluated. The main conclusions are as follows. K59 + 320 slag disposal site’s failure is mainly caused by the underlying silty soil layer with 8 m～ 10 m depth which isn’t discovered in initial. The planned slag abandonment height of 28 m is larger than the ultimate bearing height of 25 m,which is the mechanical mechanism of disaster. The shallow bad strata found is suggested to remove or replaced treatment,the deep weak strata discovered is disposed by the comprehensive measure such as the accumulated height limited combined with foundation treatment. Based on safety and economy principles,the optimal order of reinforcement schemes of K59 + 320 slag dump site is cement soil mixing pile scheme better than anti-slide pile scheme than slag barrier wall and foundation treatment scheme than micro-pile scheme.