Cerebrospinal fluid (CSF) plays an important role in the clearance system of the brain. Low b-value DTI is reported to be useful for observing the CSF flow; however, the precise flow property observed by low b-value DTI has not been fully investigated. We proposed a mathematical framework of low b-value DTI for analyzing a pseudo-random flow and applied this framework to investigation into CSF. Measured DTI shows high and anisotropic diffusivity, representing large variance of flow velocity, in some segments of CSF. It demonstrates that low b-value DTI can be used for analyzing pseudo-random flow of CSF.