Hi Jing0000,
Welcome back.
There have been several patches out for Il2 1946, which you will have to install in order before you get to the latest 4.11.1.
The disc version comes as version 4.07m so it has to be patched with 4.08m, 4.09m, 4.10m, 4.11m, and finally 4.11.1.
I don't know what version steam gives you (it may be 4.08 or 4.09) but you can see what version you have by looking at the red writing on the bottom left corner of the loading screen.
It is advisable to backup the game after installing and checking each patch, to prevent you having to start from scratch in case you get a corrupted download.
Here is a link to another forum thread about patching;
http://forum.1cpublishing.eu/showthread.php?t=31667
The patches have given us many improvements to the stock game, more maps, more aircraft, 6DOF, improved AI (this is still work in progress), to name but a few.
Hope this was useful.
PilotError.