In this work the effect of swirl is analysed in a 3 - dimensional convergent divergent supersonic nozzle on the shock structure under various back pressure conditions. The numerical analysis is carried out in a three dimensional flow field using commercial CFD tool. The three dimensional supersonic convergent divergent (CD) nozzle is modelled in ICEMCFD and the domain is discretized using hexahedral elements. The flow field through the CD nozzle is obtained by solving the governing equations namely continuity, momentum and energy equations by Finite volume discretization using commercial CFD code ANSYS FLUENT 12.0. Turbulence is taken care by shear stress transport SST - K- ω mode of closure. It was found that the effects of swirl and nozzle back pressure weaken the strength of shock -structure considerably. Increasing the back pressure influence the shock to move upstream towards throat in the divergent portion, whereas swirl stretches the shock structure axially downstream to the throat and weakens the shock strength. © Research India Publications.