The study investigates the dynamic elastic modulus and damping ratio of sand and gravel under single and bidirectional cyclic loads using a large-scale vibration triaxial test. It also analyzes the effects of confining pressure and radial cyclic stress on the dynamic parameters of sand and gravel. The results show that in the bidirectional vibration triaxial test， the axial dynamic strain of sand and gravel is less influenced by the radial dynamic stress， with the dynamic strain primarily related to the applied axial dynam? ic stress. Under both unidirectional and bidirectional vibration， the dynamic elastic modulus of sand and gravel gradually decreases with the increase of dynamic strain. Under bidirectional vibration， the decay rate of dynamic elastic modulus of sand and gravel re? mains essentially unchanged， and the dynamic modulus of bidirectional vibration is lower than that of unidirectional vibration under the same dynamic strain. The damping ratio of sand and gravel under bidirectional vibration is larger than that under unidirectional vibration， and the dynamic strain energy consumed under bidirectional vibration is larger. Based on the analysis of the maximum dy? namic elastic modulus and dynamic modulus ratio under the two test conditions， a conversion relation expressing the maximum dy? namic elastic modulus under single and double direction test conditions and a correction model of the dynamic modulus ratio and dy? namic strain in the bidirectional vibration test were established. The research results can provide a theoretical basis for the seismic design of sand and gravel in high earth-rock dams.