Mytilus coruscus is an important marine cultured shellfish in China, and it is also a fouling organism. Once the larvae of M. coruscus have the ability of the settlement and metamorphosis, they need to undergo behavior changes and body structure remodeling, complete the settlement and metamorphosis, and start benthic life. If the larvae cannot complete the settlement and metamorphosis, they eventually die. Therefore, the settlement and metamorphosis is very important for the normal development and population maintenance of M. coruscus. Previous studies have shown that biofilm can significantly improve the settlement and metamorphosis rate of larvae. In addition, lipopolysaccharide (LPS) plays an important role in the process of biofilm formation. To explore the effects of LPS on the formation of marine bacterial biofilm and the settlement and metamorphosis of mussel larvae, this study used firstly different concentrations of LPS to directly stimulate the larva of M. coruscus to observe the direct effect of LPS on larval metamorphosis. In addition, the biofilm was formed by adding different concentrations of LPS and Pseudoalteromonas marina, to analyze the changes in biological characteristics of the biofilm and the influence of the changed biofilm on the metamorphosis of the mussel larvae. The results showed that LPS at three concentrations could directly induce metamorphosis of M. coruscus larvae. The bacterial density and thickness of biofilm treated with 10.0 mg/L LPS were significantly decreased, especially the thickness of biofilm decreased by 12.1%. After being treated with 10.0 mg/L LPS, the polysaccharides and lipids in extracellular products were significantly increased, the content of colanic acid increased by 35.4%, and the induction of larval metamorphosis was also increased by 53.3%. Thus, LPS has a direct effect on the settlement and metamorphosis of M. coruscus larvae, and LPS might indirectly affect the settlement and metamorphosis of M. coruscus larvae by regulating the production of extracellular substances in the biofilm, especially colanic acid. The finding of this study is helpful for underpinng the mechanism of biofilm regulating the settlement and metamorphosis of M. coruscus, improving seedling production technology, and providing a theoretical basis for marine antifouling.