To further study comprehensive effect of compaction conditions and fines content on soil seismic stability characteristics,a series of cyclic loading tri-axial tests were carried out on soils with different gradations.The influence rules and corresponding mechanism of moisture content,dry density and saturation on undrained dynamic strength were discussed.The discrepancy of dynamic strength characteristics caused by fines content difference was analyzed.And a equation with compaction degree and saturation degree as independent variables was introduced to quantitative express dynamic strength.The results show that under a certain compaction energy,soil with the highest dry density does not necessarily have the greatest undrained dynamic strength.For the soil with high fines content,dynamic strength is determined by both compaction degree and saturation,while for the soil with low fines content,dynamic strength is only affected by compaction degree.The undrained dynamic strength of compacted soil can be estimated by equation without knowing compaction curve.This method is useful for seismic stability evaluation.