Drug resistance of pathogenic microbes is a quickly growing and extremely dangerous health threat. Bacterial infections are one of the most important causes of skin ulcers. The significant increases in the rates of infection with antibiotic- and multi-drug-resistant bacteria in recent years have hindered clinical treatment, but the effect of antibiotics is very disappointing. Therefore, we have applied ALA-PDT in the treatment of refractory infectious ulcers in clinical practice, and find that ALA-PDT is a potential modality to control Pseudomonas aeruginosa infection and can effectively kill Pseudomonas aeruginosaon chronic skin ulcers, and promote healing of chronic skin ulcers. Through in vitro experiments, we have further confirmed the elimination effect of Pseudomonas aeruginosa biofilm by ALA-PDT and its related mechanisms. And our results shows that ALA-PDT kills planktonic P. aeruginosa and viable cells in the biofilm, destroys biofilm structure, reduces virulence factor secretion, and affects QS system gene expression. These results provide further experimental evidence for the use of PDT for the clinical treatment of P. aeruginosa infections.