Abstract: Objective:To provide microscopic anatomy of the transmastoid presigmoid sinus approach(TPA) in clinical research.Methods:Fifteen cadaveric specimens(30 sides) treated with 10% formaldehyde solution were selected for microscopic anatomy studies through simulating TPA.The space-occupying lesions of petroclival area of 5 cases were resected through TPA.Results:The distances from the suprameatal spine of external auditory canal which was defined as a basis points away transverse sinus-Sigmoid corner(TSC),semicircularis canalis,trigeminal notch,arcuate eminence,outer edge of internal acoustic pore and petrous apex were 13.782.72mm,(17.821.22)mm,(47.333.11)mm,(12.181.14)mm,(31.101.28)mm and(49.112.41)mm,respectively.The distances from the leading edge of TSC which was defined as a basis points away semicircularis canalis,trigeminal notch,arcuate eminence,outer edge of internal acoustic porise,petrous apex and the longest distance the cerebellum were(14.732.74)mm,(59.142.01)mm,(8.252.67)mm,(36.482.73) mm,(60.033.66)mm and(13.881.04)mm,respectively.Five cases with space-occupying lesions of petroclival area were resected,1 case with facial paralysis aggravated and preoperative symptoms of 4 cases disappeared and no complications.Conclusions:The relation of the surface markers of temporal bone rock and internal structure can guide surgery.TPA is good operation way in processing the petroclival area lesions.