Emacs Mark Region and Scrolling Problem

The problem looks like this in emacs when I set the mark:

1. C+SPC set the mark at the beginning of the paragraph

2. Move to the end to paragraph.

3. If I need to scroll the page in step 2, the cursor will move to the current view of the emacs

4. Then I use left click to select the region between the start mark and current cursor. But I only get part of the region that in the current view.

After making me depressed a long time, I realized that the reason is due to the failing of set mark in step 1. C+SPC is not captured by Emacs, but by my Input Method.