<p>The dynamic migration behaviour of plutonium (Pu) in compacted clay was investigated by using a self-developed experimental apparatus under three distinct seepage pressures. The results demonstrate that Pu migration is governed by the water flow velocity and Pu speciation. Water flow exerts a dual influence: (i) it physically transports Pu, thereby accelerating its migration with increasing flow velocity; and (ii) dissolved oxygen within the flow could promote the oxidation of Pu(IV) to the more mobile species Pu(V) and Pu(VI). Notably, the dynamic adsorption distribution coefficien (<i>K</i>^<i>d</i>_<i>d</i>) of Pu in compacted clay was found to be an order of magnitude lower than its static adsorption distribution coefficient (<i>K</i>^<i>d</i>_<i>d</i>). Consequently, (<i>K</i>^<i>d</i>_<i>d</i>) must be incorporated into safety assessments for Pu-containing waste disposal under hydrologically active scenarios to avoid significant underestimation of Pu migration potential.</p>