Abstract: As an important part of special effects in the virtual battlefield，the effects of explosive gas play a key role in the overall system performance．It is difficult to obtain realistic picture of dynamic explosive gas because of its instantaneousness．The crucial step is to establish an appropriate model．In this paper，we present a new model，where iterated function system（ IFS） and isentropic expansion rule were introduced to describe its characteristics．Definition of explosive gas and corresponding realization algorithm are presented．As a result，a series of realistic images rendered by this approach are illustrated．