Hi Cinmoyee,
OK, so I think the problem you are seeing is that the exported image is a full resolution, whereas what you see on your screen is being limited by your level of detail. In the case of the exported image, I"m assuming the issue is that you want to get rid of the curved edges that seem to be exploding out from the network. This is coming from the fact that you have many edges between the same nodes. Cytoscape will try to make it look right by curving the edges out so that individual edges can be seen. In the limited details view, those curved edges aren't shown. There are two things you could do here. First, you could collapse multiple edges into a single edge (Edit->Remove Duplicate Edges...), which should result in no curved edges (and make things a lot faster). Second, you could explicitly set the edge bend visual property to force all of the lines to be straight. That would more closely mimic what you see in the network view.
-- scooter