The Gran Telescopio Canarias (GTC) is a Spanish initiative, open to international partnership, to construct a 10-m segmented mirror telescope at the Roque de Los Muchachos Observatory, on the Island of La Palma. The GTC first light will be at the end of 2002, while it will be fully operational at the end of 2003. The GTC Global Model (GTCGM), using MATLAB/SIMULINK, aims at verifying the design of the telescope complies with the specifications set by the GTC Project Office. The GTCGM can also provide evaluations of the individual contributions of each simulated error, for the Error Budget verification.