To assess the value of transcranial Doppler ultrasonography (TCD) in the diagnosis of low-flow internal carotid cavernous sinus fistulae (CCF). Methods: In this paper we detected the characteristic TCD change in a case of low-flow CCF diagnosed by the DSA and reviewed the relevant literature. The hemodynamic features of low-flow and high-flow CCF subtypes were compared analyzed, and the differences were summarized. Results: In the case studied, the TCD characteristic of low-flow fistula showed increased ophthalmic artery blood flow velocity, and the frequency spectrum was intracranial. Having searched relevant cases, we found characteristic TCD findings associated with high-flow CCF to be as follows: the typical TCD signs of CCF are increased blood flow velocity and decreased pulsatility index (PI) of the extracranial internal carotid artery (proximal to the fistula); blood flow velocity of the MCA and ACA is reduced; high flow velocity is found on the siphon carotid artery as well as spectrum disorder and acoustic noise, vortex flow and turbulent flow may simultaneously appear, and low-level fluctuating venous blood flow signals can be detected; the SOV has reversed blood flow with arterialization and increased flow velocity. The main TCD characteristics of low-flow CCF are as follows: there is no obvious difference between the blood flow parameters; the blood flow velocity, PI, and frequency spectrum of the basilar artery are normal and symmetric. Conclusion: Our findings highlight the value of TCD in decision-making during the screening and diagnosis of low-flow CCF.