The invention discloses a system for bluffing gas expansion for a drilling simulator, which comprises the following way (1) reading state parameters and operating orders of frontal- end outfit; (2) according to the acquired outfit state parameters and the types of the operating orders and apre-established gas expansion model, calculating data for realizing a gas expansion simulation cartoon; (3) according to a set data format, communicating with a technical graphic processor unit, swapping functional data, and also consequently finishing the cartoon representation of the gas expansion in a drilling process by the graphic processor unit; and (4) according to the set data format and the graphic processor unit for communication, swapping the state information of the cartoon. Grounded on computer stimulation technology and according to the on- point factual situations of drilling operation, pictorial stimulation of the process of generating expansion when the gas overflows in an annulus and goes overhead in the drilling process is carried out, so that the presence of tutoring training is enhanced, the training period is docked, the training effect is bettered, and the training cost is reduced.