This paper presents the mathematical modelling of the modification of the pore space geometry of a structured soil subjected to suction increase. Structured soil concepts are first introduced considering different fabric units, such as aggregates and fissures. The numerical modelling of the structural evolution is based on experimental test results in which the evolution of the structure of the samples subjected to different suctions is determined using the mercury intrusion porosimetry technique. From this information, the macro and micropore volume evolutions are determined. The results show that drying produces a reduction in the soil total porosity which mainly corresponds to a reduction of the macropore volume. Associated with this phenomenon, an increase in micropore volume is also observed. The proposed model divides pore size distribution into three pore classes (micropores, macropores and non-affected areas). Using the concept of a suction-influenced domain, the proposed model is able to reproduce the main observed fabric evolution between the saturated and dry states.