Port concrete generally suffers from chloride diffusion. To evaluate the resistance of mortar to chloride diffusion under different instantaneous loads after aggregate pretreatment，we coat the aggregate with slag powder and silica fume slurry respectively to change the roughness of aggregate. We then test the chloride migration coefficient of samples after an instantaneous load. The experimental results show that the interface performance of the aggregate is improved after pretreatment. The chloride diffusion coefficient of the mortar prepared by the pretreated aggregate is lower than that of the untreated aggregate，and the coating effect of silica fume is superior to that of slag powder. A larger load leads to a higher chloride diffusion coefficient，which endows the silica fume-coated aggregate after loading with the best resistance to chloride diffusion.