It seems that the memory usage of my JRE reaches its limitation — as we know, Flex Builder is running in JRE. Here is a simple way to solve this problem. It‘s just changing the preferences settings of Flex Builder.
Solution Summary: There are two useful arguments of JRE to control the memory usage:
I just set –Xmx to 1024m to satisfy the usage of compiling such huge Flex project.
With Flex Builder, point to the menu “Windows” at the top and open the “Preferences” dialog.
Expand the left tree as this: Java->Installed JREs. Then select the JRE being used and click Edit to open the “Edit JRE” dialog.
Then, set the Default VM arguments as “-Xmx1024m” to enlarge the memory usage limitation.