Abstract: To study the influence of dyeing on the structure and luster of seawater cultured pearls and to explore the penetration ways of dye liquor in the dyeing process of seawater cultured pearls, the present paper observes and analyzes the surface structure and internal characteristics of the seawater cultured samples before and after dyeing by using the dyeing experiment, scanning electron microscopy and gemmological microscope, measures the changes in surface reflectivity of the samples before and after dyeing by microscopic spectrophotometer-polarizing microscope, and identifies the components of the samples before and after dyeing by infrared spectroscopy.The results show that the dyes penetrate into the interior of pearls during the dyeing process mainly through the gap between the bead nucleus and the nacreous layers and the loose organic parts of the pearl surface, and then the dyes interact with the organic matter of the pearls.The brick-and-mortar structure of the pearl samples after dyeing remains unchanged.The dye particles combined with the organic matter between the crystal layers of pearl surface could fill in the gap caused by bleaching, thus the mirror effectiveness of pearl surface could be enhanced, and pearl surface luster could be improved after dyeing.