If you don't use Asian languages, then the simplest thing to do
is to remove Asian language support in Start | Control Panel |
Regional & Language Options | Languages, and to disable Asian
languages in Start | All Programs | Microsoft Office Tools |
Microsoft Office Language Settings.

If you do use Asian languages, then there are three things you
might try:
1. Click on Start | Control Panel | Regional & Language
Options | Languages | Details | Settings. Set the default input
language to English.
2. Click on Start | All Programs | Microsoft Office Tools |
Microsoft Office Language Settings | Enabled Languages tab |
Default version of Microsoft Office: English | OK.
3. Open a document in which this problem occurs. Press
Ctrl+A to select all of the text. Click on Tools | Language |
Set Language | Mark selected text as: English | uncheck the
"Detect language automatically" and "Do not check spelling or
grammar" boxes | Default | OK. If you are prompted to save
changes to your Normal.dot global template when you exit Word,
say yes.

noel wrote:

How do i change the default input language in MSWord from Chinese to English?
Because my language bar automatically switches from English to Chinese
whenever open MSWord.