Objective To study the effects from varying stenosis degrees of the mesencephalic aqueduct on intracranial cerebrospinal fluid ( CSF) flow field. Methods Based on the clinical magnetic resonance image sequences of a male volunteer, a complete normal CSF circulation model was reconstructed by using semiautomated image segmentation technique. Subsequently, eight ideal models representing different stenosis degrees of the mesencephalic aqueduct were manually created. Computational fluid dynamics (CFD) was then performed to simulate the CSF flow field in the nine models. Results The stenosis degree of the mesencephalic aqueduct was positively correlated with the maximum pressure difference between the aqueduct upstream and downstream and the maximum velocity of CSF within the stenosed aqueduct. In the normal model, the maximum pressure difference was 0. 84 Pa and the maximum velocity was 11. 4 mm / s. While in the maximum stenosed model, the maximum pressure difference and velocity were 21. 36 Pa and 60. 3 mm / s, respectively. Compared to the normal model, the maximum pressure difference and velocity were approximately increased by 25 times and 5 times, respectively. Moreover, the maximum pressure difference was inversely proportional to the stenosis area square of the aqueduct, and there was a linear relationship between the pressure difference and the quadratic the maximun CSF velocity. Conclusions The pressure difference and velocity of the stenosed mesencephalic aqueduct was not apparently increased with mild stenosis with respect to the normal aqueduct, while the great aqueductal stenosis increased the risk of hydrocephalus. This study provides a theoretical framework which contributes to understanding the development of obstructive hydrocephalus and intracranial hypertension.