This paper discusses the development of a 3D natural state model of Los Humeros Geothermal Field (LHGF), based on numerical simulations with AUTOUGH2. The model gives a good representation of the temperature distribution and the groundwater system. Hence it can be used for simulation of the production history and subsequently for simulation of proposed future exploitation scenarios. In the construction of the conceptual model, some important characteristics of the geothermal field were identified: first was the elevation of groundwater level and second was the three types of downhole temperature profiles, two of which are associated with two different geothermal reservoirs. Faults and geological units were identified, dividing the permeability structure of the model horizontally and vertically. The permeabilities of the corresponding rock-types in the model were adjusted in order to accurately calibrate the heat flow within the reservoirs, based on the temperature logs and the spatial distribution of autogenic minerals. Key features of the conceptual model are the presence of a lower and upper reservoirs in North-West zone, a continuous reservoir above 2000masl and convective behavior in the North-East and Southern zones. Also there is conductive behavior at lower temperatures in the zone outside the area enclosed by “Main Collapse”, “Los Humeros”, ” La Antigua”, ”Mastaloya” and “Las Viboras” faults.