I want to draw different sections(having different scales) in one drawing.Please guide me how to do.

In your model use all scale 1:1
in your paperspace you can create different viewports. click on the viewport and use annotation scale (bottom right) to get the scale of the viewport selected.
 
Micha

Sorry I want to make the drawing(of different scales) in model.In my opinion I will make some changes in dimension settings and there i will set my scales.Is this possible?

Just wondering why you would like to have different scales in Model space?
As this is one drawing, I don't think it is possible.
You can try if you are working in mm, to have a scale 1:1000, 1:100, 1:10 and 1:1 in your drawing by just drawing the items "bigger".