Objective To investigate the non-invasive monitoring method of cerebral edema and the combination of cerebral edema and intracranial hemorrhage (ICH) based on fNIRS. Methods A head model was established based on the visible Chinese human (VCH) datasheet. The Monte Carlo simulation was conducted to analyze the light intensity, light absorption, photon fluence and spatial sensitivity distribution of head models at different levels of cerebral edema. The change in light intensity caused by ICH was also studied. Results Light intensity is directly related to the increase in cerebrospinal fluid volume. Photons can be transmitted to brain tissue. The occurrence of ICH can significantly reduce light intensity and can be used to reflect the presence of ICH in cerebrospinal fluid. Conclusion The use of fNIRS technology to observe changes in light intensity is expected to be a simple and reliable bedside monitoring method for cerebral edema.