Cellulose rich and cellulose enriched pulps are com. important and scientifically interesting materials with a complex hierarchical fiber wall nanostructure which change with moisture sorption and swelling in water. The fiber wall building blocks and cavities are in size ranges addressable by small angle x-ray scattering (SAXS) but due to large variability in sizes and shapes, extracting quant. data about the fiber wall nanostructure from SAXS data can be challenging. For this purpose, a simulation method was developed for modeling SAXS data recorded on cellulose rich pulps. The modeling method is independent of the establishments of sep. form factors and structure factors and was used to model SAXS data recorded on dense samples. An advantage of the modeling method was that it made it possible to connect exptl. SAXS data to apparent average sizes of particles and cavities at different sample solid contents. Exptl. SAXS data could be modelled as a superposition of a limited number of simulated intensity components and gave results in qual. agreement with CP/MAS 13C-NMR data recorded on the same samples. For the water swollen samples, results obtained by the SAXS modeling method and results obtained from CP/MAS 13C-NMR measurements, agreed on the ranking of particle sizes in the different samples. The SAXS modeling method is dependent on simulations of autocorrelation functions. The time needed for simulations could be reduced by rescaling of simulated correlation functions, due to their independence of the choice of step size in real space. This way an autocorrelation function simulated for a specific sample could be used to generate SAXS intensity profiles corresponding to all length scales for that sample and used for efficient modeling of the exptl. data recorded on that sample.