Nuclear geophysics well logs allow for field exploration and development control by evaluation of the material composition of rocks. For neutron methods, the petrophysical basis for determining the lithological composition, reservoir properties, and fluid saturation is the variation in the properties of the nuclei of individual elements based on neutron characteristics and one of them is neutron slowing down length. A petrophysical model was developed of the neutron slowing down length and its application for fluid saturated reservoir rocks modeling and evaluation was provided. The proposed petrophysical model makes it possible to take into account the volume contents of individual rock components and their mineralogical composition. It can be inferred that the proposed model adequately depicts the input data and can be utilized to calculate the neutron slowing down length in reservoirs of multimineral composition and multicomponent saturation. Since the propagation of neutrons in rocks is influenced by all chemical elements, not only hydrogen, the neutron slowing down length characterizes the neutron-decelerating properties of the rock. If the neutron method readings are calibrated in units of slowing down length, the inversion of the petrophysical model enables the construction of an interpretation algorithm. In well logging and logging while drilling, stationary neutron methods are widely used. Modern tools offer azimuthal registration, thereby re-inforcing the necessity to enhance the interpretation of neutron methods. The possibility of using the developed model in conjunction with the previously developed effective porosity model to calculate the slowing down length in reservoirs with different saturations (such as bound and movable water and hudrocarbons) is shown.