How to make my master thesis defending smooth with good english speech?
Use short, simple sentences.
Write a draft script to go with your slides.
Find a friend or an editor for hire to check your draft script.
Make sure you understand each of the corrections this person provides.
Create a target listener.  Ideally, this person will be well aligned with your committee members' profiles.  Reduce the background information part of your talk as much as possible.  Include only the background information your target listener really needs to hear.
Give practice talks to friends.
Videotape one of your practice talks.  Many people gesture too much with their laser pointer or ruler, so watch out for that.
After your talk, during the Question period, make sure to repeat each and every question that is posed before you start to answer it.  This will (1) ensure you have understood the question, (2) ensure everyone in the room has heard the question, and (3) buy you thinking time.  Practice doing this.