Objective To discuss the clinical value of diluted contrast enhanced Dyna CT in evaluating direct carotid-cavernous fistula(DCCF). Methods The clinical data of 16 patients with traumatic and solo fistulous DCCF were retrospectively studied. The images by 3D rotatory digital subtraction angiography (3D-DSA) and diluted contrast enhanced Dyna CT were used for comparison and analysis of their values for diagnosis of DCCF. The comparison items included information on the orificium fistulae, the retrograde leptomeningeal venous drainage (RLVD), the draining veins and the compartment of the cavernous sinus. Results Compared with 3D rotatory DSA, Dyna CT demonstrated 21 more findings in 15 patients (93.75%), including the detection of the orificium fistulae (n=8), the RLVD (n=2), the draining veins (n=2), and compartment of the cavernous sinus (n=9), with significant difference found between Dyna CT and 3D-DSA in revealing the orificium fistulae and compartment of the cavernous sinus (P<0.05), while not in revealing RLVD and the draining veins. Conclusion Compared with 3D-DSA, Dyna CT can more effectively demonstrate the orificium fistulae and compartment of the cavernous sinus of DCCF, which may benefit the clinical diagnosis and treatment of DCCF.