To discuss the effects of photodynamic therapy (PDT) on the mainly oral cariogenic biofilm bacteria,an artificial caries model was built consistent with the physiological environment with streptococcus mutans. Hematoporyrin monomethyl ether was selected for photosensitizer. 635 nm diode laser was used for irradiation,with delivered power 10 mW and energy density 12.47 J/cm2. Fifty enamel blocks were formed artificial caries models. Separated them into five groups random,ten blocks each group:1) Group of HMME;2) Group of laser;3) Group of PDT;4) Positive control group of 0.05% chlorhexidine;and 5) Negative control group of 0.9% saline. The influence of on dental plaque oral biofilm of artificial dental caries was observed according to plate counting of bacteria method. Compared to negative control group,the number of streptococcus mutans (CFU/mL) of oral biofilm in artificial caries model of HMME group was not significant different (P>0.05),with the bactericidal rate only 0.05%;laser irradiation and 0.05% chlorhexidine made the number of streptococcus mutans of oral biofilm in artificial caries model significantly reduced (P<0.05),with the bactericidal rate 59.94% and 58.52% separately;after PDT treatment against dental caries,the number of streptococcus mutans of oral biofilm in artificial caries model significantly reduced (P<0.05),the bactericidal rate up to 99.36%. HMME-PDT is an effective method in eliminate streptococcus mutans of oral biofilm for artificial caries model. It provides an new effective approach for dental caries prevention.