The seepage experiment of the hydrophobic association polymer was carried out in the two stage series flat sand inclusion seepage model. The results showed that the hydrophobic association polymer in the two stage series possessed three different types of seepage characteristic in the porous media and associated with the permeability of the porous media; The first seepage type (I) was that the polymer had the same drag coefficient on the direction of flow when the permeability was greater than 1.8 μm2. The second seepage type (II) was that the polymer had an increase of the drag coefficient on the direction of flow when the permeability was equal to 1.8 μm2. The third seepage type (III) was that the polymer had a decrease of the drag coefficient on the direction of flow when the permeability was less than 1.8μm2. By comparison of the experimental results of single stage and two stage series plate clamp flow experiment of sand flow models, it was proved that the drag coefficient difference of the second seepage type and the third seepage type was resulted from the changes in the seepage aggregate. The seepage aggregate size changes were studied through the single-stage and two-stage tandem microporous membrane filtration experiment and dynamic light scattering experiment. The results showed that and the difference of the drag coefficient of the above mentioned two seepage types was caused by the size change of the hydrophobic association polymer in the series plate clip sand model.