The plasma in the eolian sand, included silt particle and clay particle, change easily and hugely. For studying their influences on the strength property of eolian sand, mixed silt particles and clay particles in different proportion into the eolian sand to carry out CBR test. The test result indicates that, along with the increase of silt particle and clay particle content the CBR value also increases within a certain range, which indicates the increase of silt particle and clay particle content can firstly improve the gradation of eolian sand; after the gradation is improved can obtain large compaction dry density, and at the same time also can enhance the earth strength, included the CBR value. The range of silt particle and clay particle content made the CBR value increase is also very large: ≤40% when formed under dry state, and ≤45% when formed under optimum or saturated water content; if the water content in forming could be retained at all times, the former could be ≤55% and the latter still ≤45%. The mechanism analysis further indicates that, when there were no excessive silt particles and clay particles, in the large range of silt particles and clay particles changing from small to large, the engineering nature of eolian sand will be improved due to the improvement of gradation, which is advantageous to the extensive application of dry compaction process; but the eolian sand formed by dry compaction is defective on microstructure, and so the requirements for silt particle and clay particle content should be more strict in practical works.