Objective:To investigate the effects of preventive high thoracic epidural block (PHTEB) for different periods on cerebral vasospasm (CVS) following subarachnoid hemorrhage (SAH) in rabbits.Methods: T6-7 epidural space was opened and an epidural pipe was introduced to establish PHTEB model. Ropivacaine(1 g·L-1) was injected continuously through the pipe at 1 ml/h to block T1-5 sympathetic nerves. Sixty HTEB rabbits were assigned to 6 groups (n=10 each): the normal 1 day group (N1), the normal 7 day group(N7) , SAH 1 day group (S1), SAH 7 day group (S7) , PHTEB plus SAH 1 day group (HS1), and PHTEB plus SAH 7 day group (HS7). CVS was developed by injecting non-anticoagulant autologous arterial blood (0.5 ml/kg) into the cisterna magna. Transcranial Doppler (TCD) ultrasonography was used to determine Vm of the basilar artery. The lesion and spasm of the basilar artery were observed under optical microscope. Results: Compared with group N1, Vm was significantly increased in group S1 (P<0.01) and increased in group HS1 (P<0.05). Compared with group N7, Vm was significantly increased in group S7 (P<0.05) and similar to that in group HS7 (P>0.05). Vm in group S1 was significantly increased compared with group S7 (P<0.05); and that in group HS1 was significantly increased compared with group HS7 (P<0.05). Pathological observation showed no obvious changes in group N1 and N7. The vessel wall was shrunk and the lumina became narrow in group S1 and S7. The pathologic changes in group HS1 and HS7 were slighter than those in group S1 and S7;and Group HS7 was slighter than group HS1. Conclusion: PHTEB can relieve CVS in SAH rabbits, and the relieving effect increases with time of PHTEB.