On Wed, Dec 2, 2015 at 1:03 PM, Eric S Fraga <e.fraga@ucl.ac.uk> wrote:
On Wednesday,  2 Dec 2015 at 10:46, Jinli Feng wrote:

[...]

> Thanks for the rely. I used "C-c C-e l p" to export the file. For some

You want to do "C-c C-e l P" for beamer export.  Otherwise, you get
LaTeX export.  Your output may look like beamer in that it has used the
LaTeX beamer class (because that's what you told it to do) but it did
not parse the structure of the org file.

If you use "P" instead of "p", ox-beamer will interpret the headlines
properly and you do not need to set LATEX_CLASS.

Thanks Eric. Yes, even though I thought I'd checked all the available export options, I failed to distinguish the nuances between p and P. Your initial answer pointed me to the right direction, as I found that pdflatex on the exported tex would give a different pdf from the export command (C-c C-e l p). Now one more step closer to the destination, if only I can figure out how to get the missing title and author in the pdf. 

Thanks for all the help!

You may need to add

(require 'ox-beamer)

to your emacs initialisation code.
--
: Eric S Fraga (0xFFFCF67D), Emacs 25.0.50.2, Org release_8.3.2-355-g18f083