Is it possible to choose more than one AF point when shooting a picture with DSLR?

Nikon D5100 has 11 AF point, I usually choose one point and re-frame the picture then shoot, but I'm not sure whether I can choose two points or not.

I don't think that's an option on the D5100. What you can do is use the directional keypad to chose an appropriate focus point. That's also explained really well in the manual.

Well I suppose you already know about the feature where the camera selects the auto-focus points itself, whereby the camera sometimes selects more than only one point. However I believe that you are looking for a way to have control over and use several focus points together at a time, and sadly that is not possible with a D5100 as far as I know (I have a D5000 which is very similar). You can only select one focus point at a time.

On some more professional cameras I believe it is possible to select groups of AF-points, but as said, it is probably not possible with D5100. Check the user's manual for your camera to be sure.

Lets think about this for a minute!
If you had this facility:
Lets say you select the extreme right and extreme left focus points. If the objects on the left and right are equidistant then your 2 selected focus points will lock on and successfully focus both objects. But if they are equidistant then focus on one and the other will be in focus anyway! You don't need to set 2 points.

Now if the 2 objects are at different distances from the camera - eg a person standing left screen and panoramic view right screen. If you have both points selected then they can't both focus! They would be fighting it out and the focus could never lock.

So the ability to select 2 autofocus points is pointless (!) - it either won't work or it isn't needed.

My Canon has an "A-dep" setting. It is like P mode but it selects the aperture needed to get the depth of field so as many of the 9 focus points as possible are in focus. It then sets the shutter to match - at least I think that's what it does! I've never used it:-)

Probably the simple explanation is no… You can't. The reason is you're dealing with glass and it's no flexible… So it can't focus on two subjects at the same time unless they're equal distances from the lens… It won't happen.