Abstract: A field tracer threedimension migration test in weak phreatic aquifer is conducted. It can be seen from the results of migration test of radionuclides that the peak positions of the radionuclides, 90Sr, 237Np, 238Pu and 241Am, don't move, the mass center of 90Sr, which migrates at fastest velocity among them,only moves 0.32 cm during the 1 023 days, as well as the retardation coefficients, Rd, are 4.0×102 for 90Sr, 1.6×103 for237Np, 2.7×105 for 238Pu and ∞ for 241Am, respectively according to migration velocity of mass center. It shows that loess has stronger sorption capacity for the radionuclides.