Here are below steps which am doing..
1) IActiveView av = pMapDocument.ActiveView;
2) av = (IActiveView)pMapDocument.ActiveView.FocusMap;
//stores coordinates minX, minY, maxX, maxY
3) env.PutCoords(minX, minY, maxX, maxY);
4) graphicsContainer = (ESRI.ArcGIS.Carto.IGraphicsContainer)pMap; // Explicit Cast
5) Adding all graphics - here
6) IPageLayout docPageLayout = pMapDocument.PageLayout;
av.Extent = env;
av.Extent.CenterAt(midPt);
av.Refresh();
7) ExportActiveView((IActiveView)docPageLayout, 300, 1, imgType, "D:\\", true);
Please let me know where am going wrong