Is that good to consume green tea three times a day to control blood sugar? what about the side effect for my kidneys?

Try it: I can't tell you that this interesting botanical that's supposedly shown some interesting effects in mice is an evidence-based remedy for diabetes in a human. I trust you are monitoring your sugar and if you want to add green tea to your medication & fitness regimen, you should be okay. I have not heard of this as a nephrotoxin, but beware -- "herbal remedies" aren't what they're labeled to be.

Poor substitute: As much as i like green tea it is a poor substitute for true control of blood glucose. There should be no significant effet on the kidneys, but there should not be much effect on blood sugar either.