Abstract: Through the experiment,the compaction characteristics of Yellow River silty soil stabilized with lime-flyash were studied,and the microstructure of Yellow River silty soil was analyzed with the electronic microscope.The influence of compactness and compaction water ratio to the strength of lime-flyash soil was studied,and the key factors to compaction and the influence were analyzed.The reasonable compaction craft of construction was put forward through the in-situ tests.It was indicated that grain of Yellow River silty soil was of high psephicity and low surface strengths because of the long transport function of the water and a great deal of sphericity silty particle in flyash.It was difficult to form available contact between grains and to be rolled well.The low degree of compaction and the high compaction water ratio could reduce the strength of lime-flyash soil obviously.As for the Yellow River silty soil stabilized with lime-flyash,the grain size of 0.005 mm was the limiting grade that reflected the function of filling.The content of <0.005 mm grain and lime-flyash could influenced the optimum water content and the maximum dry density significantly,but the influence of lime-flyash ratio（1∶4¹∶2） was not obvious.Silt stabilized with lime-flyash was sensitive to amplitude and frequencies of vibration,and high frequency and hard oscillation could attain the degree of compaction of 98%.