Taking Zhuyu reservoir in Shannan of Tibet as the test site, the authors collected soil samples for laboratory analysis, and devised infiltration-clogging equipment for laboratory test to research the effect of clogging process on permeability of loose dam foundation of plateau reservoir. Through laboratory test, the soil can cause clogging effect by itself, and the effect of clogging is relative to the water pressure. The clogging effect can be caused obviously by adding fine particles, and the clogging effect of the particles with 0.063-0.25 mm diameter is best, which verifies the rationality of the optimal diameter interval. It provides the realistic significance for the anti-seepage of the plateau reservoir dam foundation.