Objective To investigate the effect of selective lateral episiotomy on perineal body and pelvic floor function. Methods The primiparas who delivered naturally in Guangzhou Red Cross Hospital from January 2018 to December 2019 were selected as the research subjects. The research group were given selective lateral episiotomy, while the control group were given conventional treatment. The incidence of perineal laceration, pelvic floor muscle strength lower than grade 3, the POPQ score and levator ani hiatus dilatation were analyzed. Chi-square test was used to analyze the incidence of the two groups. Results The incidence of perineal laceration in the research group was 2.5% vs 56.22% in the control group(χ²=53.14, P<0.05). The incidence of pelvic floor muscle(group I) strength lower than grade 3 in the research group was 30% vs 49% in the control group(χ²=9.03, P<0.05). The incidence of pelvic floor muscle(group II) strength lower than grade 3 in the research group was 23% vs 38% in the control group(χ²=5.96, P<0.05). The rate of the incidence of POPQ 0 in the research group was 26.25% vs 12.5% in the control group (χ²=4.84,P＜0.05). The incidence of levator ani hiatus dilatation in the research group was 16.25%, while 5% in the control group (χ²=5.33, P<0.05). Conclusion Compared with conventional treatment group, selective lateral episiotomy group has a lower incidence of perineal laceration and pelvic floor muscle strength lower than grade 3. Selective lateral episiotomy group has a higher incidence of POPQ 0 and no levator ani hiatus dilatation. Selective lateral episiotomy can protect the perineal body and pelvic floor function.