I like green tea drink it often diet green tea is it ok?

Overhyped. Green tea is the latest in a long line of overhyped nutritional products. Claims include weight loss, better health, longer life, better endurance. Do not believe the hype. Yes green tea contains some anti-oxidants and phytonutrients, but it still contains caffiene which is a stimulant and has diuretic properties. Too much green tea is not good for you.
OK but... Green tea is ok and so is the green tea diet, except there have been cases of acute liver failure described that left people handicapped and some even died, so if you decide to do a green tea diet, you will need to get your green tea from a reputable source (although, even then, it is not guaranteed you are fully protected). Green tea for drinking is usually fine.