Two soils (clay loam and sandy loam) and three addition levels of PAM (0, 22.5, 45 kg/hm²) were used to measure the dynamic changes of soil saturated hydraulic conductivity (K_s) under constant water flow (10.25 mm/h), the content and stability of soil aggregates and thus to investigate the mechanisms for the effect of the dissolution time of PAM on K_s. Results showed that K_s decreased as the dissolving time of PAM increased, and finally researched a stable state. When the dissolving time of PAM was shorter, the K_s of the PAM treatment was higher than that of control. The sandy loam soil with PAM of 45 kg/hm² had the highest grow rate of K_s, and the K_s was increased by 26.87% compared with control. The K_s changed with the amount of PAM added significantly (P<0.05). PAM stabilized the aggregate structure of the soils, increased the amount of water-stable aggregate, and thus improved the K_s. The amount of the water-stable aggregate of > 0.25mm for the treatment with 45 kg/hm² of PAM added was 8.91% more than the control in sandy loam soil, while that for clay loam soil increased by 32.54%. When the dissolving time of PAM was long enough, the K_s of PAM treatment was significant lower than control, and the largest reduction was observed in the treatment with 45 kg/hm² of PAM in clay loam soil, and the K_s was decreased by 10.86% compared with control. However, the K_s did not change with the amount of PAM added significantly. For the related mechanisms, PAM increased contents and stability of soil aggregates and thus improved K_s. On the other hand, after PAM dissolving in water, the solution became glutinous. PAM also adsorbed soil particles and blocked soil pore and thus decreased the K_s. We found that PAM improved the structure of sandy loam soil better than that of clay loam soil. The study will provide a theoretical basis for improving soil transparent performance with PAM.