We aim to investigate the clinial value of 4D flow MRI in assessing cerebrospinal fluid(CSF)dynamics. The optimal velocity encoding factor(VENC) and high test-retest reproducibility was firstly obtained in CSF measurements for healthy volunteers. Ensured by thses, 4D flow MRI has been further applied to evaluate the CSF dynamics for patients with obstructive hydrocephalus before and after endoscopic three ventriculostomy(ETV). Notable cerebrospinal fluid flow at the stoma has been found, indicating that a new cerebrospinal fluid circulation pathway was established. Our study thus demonstrated that 4D flow MRI is an effective tool to assess CSF dynamics quantitively.