Hi jinhui.wu,
What is the name & version of the toolbox you are using ?
What is the return value of this command license('checkout', 'real-time_workshop') in your Matlab command prompt ?
If you don't see 1 as the return value, you are probably not seeing the Code Generation pane in the Configuration Parameters window because Simulink is unable to check out a license for Simulink Embedded Coder (formerly known as Real-Time Workshop).
Please run command ver and paste its output here as well.
Hope this helps!
Daniel