Abstract: The supersonic nozzle is a new apparatus which can be used to condense and separate water and heavy hydrocarbons from natural gas. The swirling separation of natural gas in the convergent-divergent nozzle was numerically simulated based on a new design which incorporates a central body. Axial distribution of the main parameters of gas flow was investigated, while the basic parameters of gas flow were obtained as functions of radius at the nozzle exit. The effect of the nozzle geometry on the swirling separation was analyzed. The numerical results show that water and heavy hydrocarbons can be condensed and separated from natural gas under the combined effect of the low temperature (−80 °C) and the centrifugal field (482,400g, g is the acceleration of gravity). The gas dynamic parameters are uniformly distributed correspondingly in the radial central region of the channel, for example the distribution range of the static temperature and the centrifugal acceleration are from −80 to −55 °C and 220,000g to 500,000g, respectively, which would create good conditions for the cyclone separation of the liquids. However, high gradients of gas dynamic parameters near the channel walls may impair the process of separation. The geometry of the nozzle has a great influence on the separation performance. Increasing the nozzle convergent angle can improve the separation efficiency. The swirling natural gas can be well separated when the divergent angle takes values from 4° to 12° in the convergent-divergent nozzle.