A porosimetry simulator associated with a tridimensional pore network model was developed. This simulator, presented in two joint papers, is used to infer the actual pore size distribution of a catalyst particle by means of an iterative method. In this first paper, the network model and porosimetry simulator are introduced and a sensitivity study of the simulator to the model parameters is performed. These parameters were divided in two main groups. The first relates to the spatial arrangement of the three-dimensional pore network and includes the number of pores, the mean coordination number, the accessibility, and the network geometry. The second group is related to the characteristics of the pore size distribution, namely, its spreading, symmetry, and number of modes.