The effect of tooth preparation on the gingival crevicular flora of abutment teeth during porcelain veneer treatment is not clear. The purpose of the present study was to analyze the difference between prepared porcelain veneers and unprepared porcelain veneers on gingival crevicular flora. High-throughput sequencing was used in the present study. A total of 20 patients (40 anterior teeth) with veneer restoration of anterior teeth were enrolled. They were divided into two groups: The prepared porcelain veneer group (group P, 11 cases, 19 anterior teeth) and unprepared porcelain veneer group (group U, 9 cases, 21 anterior teeth). After 2 years of follow-up, the restoration and healthy natural gingival crevicular fluid were collected to extract bacterial DNA. 16S ribosomal DNA high-throughput sequencing technique was used to compare the diversity of gingival sulcus flora structure between the prepared porcelain veneer and unprepared porcelain veneer groups. In addition, a healthy control group (group H) was also used for comparison. The Shannon index of the group U was lower than that of group H and group P. The abundance of Proteus in group U was higher than that in group H and group P at the phylum level (P<0.05). At the genus level, the abundance of Porphyromonas, Prevotella and Actinomycetes in group U was significantly higher than that in group H and group P (P<0.05). Compared with the group P, the bacterial diversity of the group U was lower, and the proportion of gingival sulcus pathogenic bacteria was higher. The unprepared porcelain veneer had a certain adverse effect on the periodontal tissue.