Abstract: The dynamic triaxial test is carried out on the saturated intact loess sample with dynamic triaxial apparatus on the drainage condition. And analyze the characteristics of the deformation, pore pressure, hysteresis loop and microstructure of the sample. The analysis results shows: the deformation stages on the drainage condition is obviously different from the three stages on undrainage condition, the pore pressure is on a stable level during the experiment, the hysteresis loops are similar in the vibration times of N=1,N=50 and N=100,but the similarity is a bit low compared with the traditional oval-shaped hysteresis loops. The microstructure analysis tests were obtained with SEM and Mercury porosimetry analyzer. The analysis result shows that the micro-structure of the soil samples, the contact between the particles and the size of the pores all change significantly. The changes of soil particles before and after the dynamic triaxial test are obtained by analyzing the results of microstructure tests. The main conclusions about the microstructure are as followings: the relative statuses between the soil particles change from a relatively loose state into a relatively dense state, the contact relationship from scaffold contact become to mosaic contact and the contact area increase after the test, the percentage of various pore diameter change greatly and the most obvious changes are the big pore diameter. The number of large pores obviously decreases and small and micro pores increases in the number.