The ANTARES Collaboration is building an underwater neutrino telescope in the Mediterranean sea. The first full 480m line was connected to the shore station in March 2006. The full Monte Carlo simulation chain and offline software structure of the experiment is presented. The offline software structure consists of two main parts: the first concerns the generation of the Monte Carlo events in the detector and the cligitisation and filtering of the signals, while the second concerns offline event reconstruction of both Monte Carlo events and real data. The expected performances of the detector obtained from this accurate simulation procedure are also presented and discussed. (c) 2006 Elsevier B.V. All rights reserved.