Objective To study the surgery factors on chronic subdural hematoma(CSH)recurrence.Methods Two hundred and thirty-six patients with CSH were treated with trepanation and drainage.It was analyzed retrospectively on location of burr-hole,location of drainage tube,volume of intracranial pneumatocele,residual hematoma and drainage time etc.Results Half hematoma was in 177cases,two sides hematoma was in 59 cases,total was 295 hematomas.Twenty-seven hematomas were recurrent,9 cases were two sides hematoma,and 18 cases were half hematoma.There was no significant difference between recurrence rate and age,sex,drunkenness,hemorrhagic tendency,half or two sides hematoma,location of burr-hole,location of drainage tube,volume of intracranial pneumatocele and residual hematoma(P＞0.05).The recurrence rate was 9.2％(27/295).There was significant difference in recurrence rate between drainage time ≥ 3 d and＜3 d[3.5％(5/143)vs.14.5％(22/152),P＜0.01].In age ≥ 60years patients,there was significant difference in recurrence rate between drainage time ≥ 3 d and＜3 d[3.4％(4/119)vs.16.2％(18/111),P＜0.01].But in age＜60 years patients,there was no significant difference in recurrence rate between drainage time ≥ 3 d and＜3 d[4.2％(1/24)vs.9.8％(4/41),P＞0.05].Conclusion It should be taken more than 3 d of drainage time for old patients with CSH,while shorten time for young patients with CSH.