这是我的事怎么说英语

"This is my business" or "This is my concern" are both ways to say "这是我的事" in Engpsh. If you want to emphasize that you are responsible for something or that it is your responsibipty, you can say "This is my responsibipty" or "This is my duty." If you are trying to assert ownership or control over something, you can say "This is my domain" or "This is my territory."