Objective To investigate the preventive effects of lamivudine combined with chemotherapy drugs on hepatitis B virus reactivation in patients with HBV infection and tumor. Methods From July 2014 to February 2017,a total of one hundred and twenty patients with HBV infection and tumor in Nanchong Central Hospital were selected and were divided into the observation group and control group with 60 cases in each group. The control group received conventional chemotherapy and liver protection treatment,the observation group was given lamivudine prophylaxis treatment(100 mg/d,1 time/d) based on the treatment in the control group, two groups were treated for 8 weeks. Results The rates of hepatitis B virus reactivation in the observation group and the control group were 5. 0％(3/60) and 33. 3％(20/60),respectively,and the difference between the two groups was statistically significant (χ2=15. 692,P<0. 05) . There was no significant difference in serum glutamic acid transferase and aspartic transferase in the patients before and after treatment ( P>0. 05 ) , and the control group showed an upward trend ( P<0. 05) . After treatment,the serum ALT and AST in the observation group ((31. 98±6. 33)U/L,(26. 38±4. 98)U/L) were lower than those in the control group((43. 89±6. 73)U/L, (51. 78±5. 99)U/L)(t=8. 294,11. 842,P<0. 05). After treatment,the HBV DNA in the observation group and the control group((0. 16±0. 04) ×103copies/ml,(5. 02±1. 72) ×103copies/ml) were lower than those before treatment ((14. 55±2. 14)×103copies/ml,(14. 09±1. 98 copies/ml )(t=25. 498,8. 142,P<0. 05),and the HBV DNA in the observation group after treatment was also lower than that of the control group. The difference between the two groups was statistically significant ( t=24. 292,P<0. 05) . Conclusion Lamivudine combined with chemotherapy drugs used in patients with HBV infection and tumor can prevent hepatitis B virus reactivation,it does not affect the patient′s liver function,it can inhibit the replication of hepatitis B virus,so it has good application values.