Abstract: From the results of two kinds of radionuclide migration tests in unsaturated loess conducted in the field and laboratory, it can be seen that loess has stronger sorption capacity for~85Sr; retardation coefficient, R_d, of~85Sr increases with water content θ rather than a constant; R_d derived according to conventional equation from distribution coefficient, k_d, obtained by batch in laboratory is more than the measured results; variation trend of the derived R_d with θ in unsaturated loess is contrary to the measured results; lateral concentration distribution variance, σ~2_y, is equivalent to longitudinal concentration distribution variance, σ~2_x, and can't be neglected under natural rainfall condition; rainfall rate affects obviously longitudinal expansion of~85Sr rather than lateral one; moreover, migration fast composition of~85Sr affects conservative level of assessment results. The characteristics mentioned above would considerably affect the predicted concentration of~85Sr at the concerned place towards lower reaches and hence affect considerably magnitude of potential risk to human.