Objective To investigate the change of sperm mitochondrial membrane potential in obese male infertility patients,and to explore the re?lationship of sperm mitochondrial membrane potential with the reactive oxygen species and free fatty acids in seminal plasma. Methods According to the research conditions,samples were randomly selected by cluster sampling from outpatient,and divided into normal body mass index fertile men as control group(n=51),normal body mass index infertile group(n=36),overweight infertile group(n=44),and obesity infertile group(n=45). Semen routine analysis was performed. Free fatty acid and reactive oxygen species in the seminal plasma was determined by ELSA method,sperm mitochondrial membrane potential was determined by flow cytometry. Results The rate of normal sperm mitochondrial membrane potential in nor?mal weight infertility(27.34%±13.38%),overweight infertility(28.26%±9.76%),obesity infertility group(25.27%±7.51%)were lower than the control group(35.12%±15.90%),the difference was statistically significant(P<0.05). Although obesity infertility group normal rate of mitochon?drial membrane potential were lower than normal weight infertility group and the overweight infertility group,but there was no statistically significant difference. The rate of sperm normal mitochondrial membrane potential was positively correlated with the rate of sperm progressive motility(r=0.29, P<0.01). Free fatty acid was positively correlated with reactive oxygen species in seminal plasma(r=0.30,P<0.01),reactive oxygen species in seminal plasma was negatively correlated with sperm normal mitochondrial membrane potential(r=-0.24,P<0.01). Conclusion Free fatty acid was elevated in the seminal plasma of overweight and obese patients with male infertility,which causes increased reactive oxygen species,reduced mitochondrial membrane potential,and eventually lead to the decline of sperm movement ability. Patients undergoing the treatment should be ad?vised to reduce the high fat diet and perform proper exercise.