Objective To investigate the related factors affecting the postoperative drainage volume of unilateral biportal endoscopy(UBE).Methods 60 patients were divided into the high drainage volume group(n=30)and the low drainage volume group(n=30)based on the median drainage volume(50 mL).Sex,age,surgical segment,history of hypertension,history of diabetes mellitus,body mass index(BMI),history of long-term anticoagulant therapy and history of osteoporosis(t<2.5)were recorded and compared between the two groups.Results The increase of postoperative drainage volume was significantly correlated with L4~5(P=0.017),BMI ≥27(P=0.047),history of hypertension(P=0.040).Age ≥60 years,sex,osteoporosis history(t<2.5)showed no statistically significant differences(P>0.05).Conclusion L4~5,BMI ≥27,hypertension history are the risk factors of increasing drainage volume after UBE.The patients with L4~5,BMI ≥27 and hypertension history should be given intensive medical care before operation,and necessary intervention measures should be taken to prevent the occurrence of postoperative complications.