I want to come for training in china, should I change my money before going? I have master card.

Harrison, you can take some changes in case you make calls or catch a taxi. But I don't think you need to change all your money into CNY. You know, Chinese customs just allows passengers to take CNY 20000 or USD 5000 in cash. Mastercard can't be accepted at many Chinese banks. You can withdraw your money after you arrive.