Research on the polymerization of dopamine and its modification on the surface of materials has received extensive attention. In this work, the process of laccase catalyzing the rapid polymerization of dopamine and in situ dyeing of silk fabric were studied. The results showed that laccase catalyzed dyeing for 3 h under acidic conditions could achieve the dyeing effect of 24 h under an alkaline environment, and the enzyme catalyzed polydopamine showed better deposition uniformity on the substrate surface. According to molecular simulation analysis, dopamine oligomers were easily combined with the amorphous regions of silk fibroin, and dopamine oligomers and amino acids of silk fibroin could form hydrogen bonds and π–π stacking interactions. Dopamine oligomers could form intermolecular and intramolecular hydrogen bonds through amino groups and hydroxyl groups. In addition, dopamine oligomers would aggregate in the process of binding to silk fibroin and adsorbed to the surface of silk fibroin in the form of aggregates, and Michael addition reaction would also occur between dopamine oligomers and silk fibroin. Finally, the silk fabrics loaded with polydopamine were reacted with different kinds of metal salt solutions to form particles with different morphologies and crystal structures on the surface of the silk fibers, and the modified silk fabrics showed good hydrophobicity.