Abstract: In order to study the deformation characteristics of soft soil under traffic loading, dynamic triaxial tests were performed for clay sampled from Qianhai District in Shenzhen. After the dynamic triaxial test, samples were sliced and scanned by scanning electron microscope and the fractal theory was used to explain the deformation mechanism. The test results showed that when confining pressure is 100~150 kPa and frequency is 0.5~1.0 Hz, the critical dynamic stress ratio will be 0.2~0.3; however when confining pressure is 100 kPa and frequency is 0.5 Hz, the critical dynamic stress ratio will be 0.15~0.20. When the cyclic stress ratio was lower than the critical value, the development rate of axial strain increases exponentially with increase of the dynamic stress ratio. The larger confining pressure and smaller vibration frequency were, the faster the axial strain developed. Through analysis of the microstructure parameters, it was found that the increase of confining pressure would make the particles more compacted, while the increase of cyclic stress ratio and frequency would make soil particles more fragile and the pore more easily filled by smaller particles.