If i bring more than 20,000 yuan what document is needed and will they tax me or what

Jack, you'd better not take more than CNY 20000 into China. You won't be taxed. But you can't take extra money into China. According to the customs, your extra money might be sent back to Singapore. If you plan to take more than CNY 20000, I suggest you put your money in your account and then withdraw it when you arrive in China. This won't cause any trouble when you pass the customs.