Objective To explore the cause of acute urinary retention (AUR) ,the functional change of bladder detrusor. Methods The clinical data in 178 patients with AUR combined with urodynamic study were retrospectively analyzed. Results In male patients,the main cause of AUR was bladder oudet obstruction(BOO) ,the percent was 60.63%(77/127) ,in age more than 50 years old patients, while, in age less than 50 years old patients,the main cause was detrusor arcflexia (DUA), the percent was 72.55% (37/51), because of trauma of Iumbosacral vertebrae. In the female patients, the main cause of AUR was DUA. Between male and female patients with age more than 50 years old, there was significant difference in the cases of low compliance and DUA (P < 0.01) ,unstable bladder and BOO (P < 0.05). Conclusions The main cause of AUR in elderly male patients is BOO, which induces low eompliance and unstable bladder. While the main cause of AUR in female patients and young-middle age male is DUA .The function of detrusor changes differently with various causes.