Due　to　the　long-term　effect　of　cyclic　traffic　loads,　the　accumulated　deformation　of　red　clay　subgrades　is　increasing,　strength　is　decreasing,　and　problems　such　as　uneven　settlement　are　occurring.　In　order　to　improve　the　stability　and　durability　of　red　clay　subgrade,　this　paper　analyzes　the　effects　of　cyclic　stress　ratios　and　compactness　on　the　development　of　the　dynamic　elastic　modulus　of　saturated　red　clay.　This　is　achieved　through　dynamic　triaxial　tests　on　red　clay　in　the　Qingyuan　County,　Zhejiang　Province,　China.　The　results　show　that　the　saturated　red　clay　has　an　attenuation　threshold　cyclic　stress　ratio　under　cyclic　loading.　The　attenuation　threshold　cyclic　stress　ratio　prediction　models　were　constructed　based　on　the　confining　pressure　and　compactness,　respectively.　By　introducing　the　concept　of　a　relative　cyclic　stress　ratio,　the　prediction　model　of　the　dynamic　elastic　modulus　of　saturated　red　clay　(as　based　on　cyclic　vibration　times　and　close　cyclic　stress　ratio)　is　constructed.　The　model　realizes　the　prediction　of　the　dynamic　elastic　modulus　of　red　clay　under　arbitrary　cyclic　vibration　times　via　the　initial　cyclic　stress　ratio,　compactness,　and　other　parameters.　It　provides　a　theoretical　basis　for　rationally　evaluating　the　dynamic　stability　of　red　clay　subgrade　under　cyclic　loading.