The solid-solution partitioning of heavy metals in paddy soil is of great importance to evaluate their availability. It has been well established that phosphate can passivate most of Pb in soil by precipitation. However, it might also facilitate the dissolution of heavy metals in the soil and thus increase their environmental risk, and the initial reason for this is still unclear. To obtain an overall insight in the effect of phosphate in the distribution of Pb in paddy soil, a culture experiment was performed with phosphate added, EDTA as well as Diffusive gradients in thin films (DGT) and in-situ solution extraction methods were used to represent different available Pb content. Supplement of KH₂PO₄ significantly increased the content of Pb and Fe/Al in soil solution while showed no influence on the DGT-extracted Pb, which means the increase of soluble Pb might be due to an increase of complex Pb in soil solution. In addition, the amount of Al in colloids separated from soil solution were also enhanced with KH₂PO₄ treated, which might elevate the possibility for the combination of colloids and Pb²⁺. Moreover, a change of surface roughness of soil aggregates in KH₂PO₄ treated group was observed by scanning electron microscope (SEM), and this was conducive for soil solid to retain more Pb with more adsorption sites. Otherwise, Fourier transform infrared spectrometer (FTIR) combined X-ray absorption near-edge spectroscopy (XANES) analyses claimed that flooding condition promoted the transformation of inorganic-P to organic-P, the latter of which possibly participated in the complexation of Pb in soil. As above, the addition of phosphate (KH₂PO₄) in soil could enhance the retention of Pb in soil solid by precipitating with Pb and increasing the surface-adsorption capacity of soil aggregates, thus immobilizing most of Pb in soil solid. However, it might also elevate the mobilization of Pb by accelerating the dissolution of metal ions (i.e. Fe, Al) and increasing the amount of colloids, which could combine with Pb and increase its mobility in soil solution.