The red sandstone residual soil subgrade after a continuous rainfall will form a transient saturated zone， and the soil backbone curve，dynamic elastic modulus and damping ratio are the key factors for analyzing the dy- namic characteristics of the subgrade． In order to study the dynamic characteristics of red sandstone residual soil subgrade in transient saturated zone under heavy-haul train load conditions，dynamic tri-axial tests were carried out with sand and different content of red clay remolded soil samples． The effects of fines content and confining pressure on backbone curve，dynamic elastic modulus and damping ratio of soil in transient saturated zone were discussed． The results show that: the backbone curve of sand with fines content conforms to Konder hyperbolic model; the in- fluence of fines content on the dynamic elastic modulus and damping ratio is not monotonic，but there is a threshold ( about 20% ) ; the variation trends of dynamic elastic modulus and damping ratio negatively related with fines con- tent around the threshold; confining pressure has a significant effect on dynamic elastic modulus and damping ratio of soil: with the increase of confining pressure，the dynamic elastic modulus increases and the damping ratio de- creases．