Abstract: The strength of subgrade silt is easily damaged by loads such as earthquake and vehicle vibration.Traditional materials such as cement and lime are usually used to improve the silt,but it causes irreversible damage to the environment.Therefore,it is very necessary to study the dynamic strength characteristics and mechanism of silt improved by environmentally friendly biopolymer-xanthan gum.A series of microscopic analyses and dynamic strength tests were conducted on xanthan gum improved silt by varying the content of xanthan gum using scanning electron microscope and dynamic triaxial instrument.The test results show that the dynamic strength curve conforms to the power function relationship and shifts upward with the increase of xanthan gum content.The dynamic cohesion increases with the increase of xanthan gum content,and the strengthening effect tends to be smooth when the content is larger; while the dynamic internal friction angle is less affected by the content of xanthan gum.The microscopic analysis shows that with the increase of xanthan gum content,xanthan gum effectively fills the pores between soil particles and adheres to the surface of soil particles to form fibrous and reticular structures,which enhances the association ability between soil particles and leads to the increase of dynamic strength and dynamic cohesion of improved silt.The above research results can provide scientific basis for the design and construction of related geotechnical projects,and meet the needs of ecological protection and high-quality development strategy in the Yellow River basin.