I will have a Viva in January next year. But I'm so worry about the result. I would like how much possibility that people fail viva or get MPhil rather than PhD. I'm quite worry because English language is not my first language and actually my speaking is quite poor; thus sometimes I may cannot not explain somthing that is in my brain explicitly.

Well, in that case you should start improving your proficiency level.
If it's in January you still got 4 weeks or more.
Read English books-out loud (when u r alone). After 500 pages and one week you will be amazed how much your English has improved.

Did you proofread your thesis before submission?