Many diseases are related to cerebrospinal .uid (CSF) hydrodynamics. Therefore, understanding the hydrodynamics of CSF .ow and intracranial pressure is helpful for obtaining deeper knowledge of pathological processes and providing better treatments. Furthermore, engineering a reliable computational method is promising approach for fabricating in vitro models which is essential for inventing generic medicines.  A Fluid-Solid Interaction (FSI)model was constructed to simulate CSF .ow. An important problem in modeling the CSF .ow is the diastolic back .ow. In this article, using both rigid and .exible conditions for ventricular system allowed us to evaluate the effect of surrounding brain tissue. Our model assumed an elastic wall for the ventricles and a pulsatile CSF input as its boundary conditions. A comparison of the results and the experimental data was done. The .exible model gave better results because it could reproduce the diastolic back .ow mentioned in clinical research studies. The previous rigid models have ignored the brain parenchyma interaction with CSF and so had not reported the back .ow during the diastolic time.  In this computational .uid dynamic (CFD) analysis, the CSF pressure and .ow velocity in different areas were concordant with the experimental data.