Abstract: The sand-fines mixtures are widely distributed in hydraulic fill soil and may be subjected to the cyclic action of wave and vehicle loads during their long-term service. It is very important to know the dynamic pore water pressure changing characteristics of the sand-fines mixtures for evaluating the safety and stability of hydraulic fill soil under cyclic loading. The consolidated undrained cyclic triaxial tests are carried out on the saturated reconstituted sand-clay and sand-silt-clay mixtures to investigate the development features of dynamic pore water pressure of mixed soil with different clay contents, fines contents, clay silt ratios and void ratios. By combining with the optical microscope images of soil particles and the theory of soil particles occurrence modes, the influence laws and mechanisms of clay content, fines content, clay silt ratio and void ratio on the dynamic pore water pressure of mixed soils are revealed. It is find that for the sand-clay mixtures (constant e and constant e_s), with the increasing clay contents, the fluctuation growth trend of dynamic pore water pressure at the later stage of vibration increases and weakens respectively. For the sand-silt-clay mixtures, with the increasing silt contents (decreasing clay contents), the fluctuation growth trend of the dynamic pore water pressure at the later stage of vibration of specimens with FC of 5% changes nonmonotonously. While the fluctuation growth trend of the dynamic pore water pressure at the later stage of vibration of specimens with FC of 10% increases monotonically under different void ratios. The Mod-Baziar model applied to the development of dynamic pore water pressure of sand-clay mixtures and sand-silt-clay mixtures is proposed, which extends the prediction range of dynamic pore water pressure and has higher prediction accuracy. The Mod-Baziar model can better reflect the overall development trend and detail change at the later stage of dynamic pore water pressure. By comparing the values of each parameter in the Mod-Baziar model, it is found that when the Mod-Baziar model is used to predict the dynamic pore water pressure of sand, sand-clay mixtures and sand-silt-clay mixtures with different void ratios respectively, the value range of each parameter in the model increases successively. The preliminary analysis suggests that the above results are attributed to the complex bonding, friction and filling between different particles.