Abstract: Objective To explore the mechanism of benzene and formaldehyde joint damage through the study of benzene and formaldehyde jointly infected in male mice testis and sperm damage. Methods Fourty SPF male mice were randomly divided into 4 groups,control group(A group),benzene respectively separate infected group(B group),formaldehyde infected group(C group),benzene and formaldehyde jointly infected group(D group),10 mice in each group.The mice in A group were intragastric saline and vegetable oil.The mice in B group were intragastric benzene 200 mg/(kg.bw).The mice in C group were intragastric formaldehyde 10 mg/(kg.bw).The mice in D group were intragastric benzene with 200 mg/(kg.bw)+formaldehyde 10 mg/(kg.bw).Each groups were exposed for 5 days,then to weigh after 30 days and be killed,to separate bilateral testes measure its testicular viscera coefficient,optical microscope sperm counts,dead sperm and sperm deformity in mice.According to the conventional method of making testicular tissue pathological slices,HE dye rear under a microscope to observe the testicular tissue pathological changes.Use the kits testicular T-AOC and Na⁺-K⁺ atpase activity.The experimental data were analyzed using SPSS 17.0. Results Body weight and testis organ coefficient of D group exposed mice were lower than A,B,C group(P<0.05).Compared with the A group and B,C group,D group mice sperm count reduced[14.9/(10⁷·g epididymitis)],mortality(45.17%),deformity rate(58.33%) were increased(P<0.05);B,C and D group in mices,were showed different degree of pathological damages,the D group mice were damaged obviously;D groups mice testis T-AOC,Na⁺-K⁺-ATP were lower than the B,C groups,its difference has statistics significance(P<0.05). Conclusion The combined toxicity of benzene and formaldehyde have obvious synergistic effect on testis and sperm damage in mice;the injury may reduce the inhibiting ability of mice testicle cell and inhibiting ATP enzyme activity.