The parameters of one dimensional steady flow of a Van der Waals gas in a nozzle of variable cross section A(x) for isentropic and thermostatical expansion flow are obtained by numerical methods in this paper. The solutions are compared with the theorical solutions of pefect gas and the deviations of the Mach number, density, pressure and temperature ratios are obtained. The obtained conclusions is significative for directing the development of technology of cryogenic and hypersonic tunnels, and the design for rocket engine.