To reveal the effect of in-situ coverage of nano materials on heavy metals in surface sediments, the incubation experiments of in-situ sediment columns were carried out. Using micro-interface analysis technique, the high-resolution dialysis(HR-Peeper)technique and the diffusive gradients in thin films(DGT), the influence mechanisms of in-situ coverage of Fe₃O₄ nanoparticles on the release of Co and Ni from surface sediments were dissected. The results shows that the pH of the sediment covered by the nano-Fe₃O₄ gradually increased compared to that of the control group, while the Eh value decreased first and then increased. The coverage of nano-Fe₃O₄ can effectively adsorb the dissolved Co and the dissolved Ni in the pore water, and the maximum effective adsorption rates of dissolved Co and dissolved Ni in the pore water were 27. 07% and 26. 42%, respectively, with effective effect depths of 30 mm and 10 mm, respectively. The coverage of nano-Fe₃O₄ effectively inhibit the diffusion of labile Co/ Ni in sediments to overlying water and reduced the content of labile Co/Ni in sediments by 50. 26% and 15. 31%, respectively.