Thank you, i have updated to SP1 and the problem is resolved.

I am currectly running on Windows 7 (No Service Pack are currently installed)
I have set compatibility mode for the game to Vista Sp 2.

Below are my PC spec:
Operating System: Windows 7 Ultimate 64-bit (6.1, Build 7600) (7600.win7_rtm.090713-1255)
Processor: Intel(R) Core(TM) i5-2500 CPU @ 3.30GHz ...

The game seems working fine until i finished researching the Train tech and the new objective to collect bunch of materials show up, the game will then lag very badly.
Here is my save file https://www.dropbox.com/s/424m67ic524bo ... 3.zip?dl=0