The tip is part of the salary of the workers of any bar or restaurant. In many countries it is compulsory, in another optional but almost obligatory and in others, few, it does not exist. This is the case of Japan, where you really save a lot of money by not leaving that extra. But How is the tip issue in China? Exists? How should we calculate it?
There is a tip in China though not the most common practice of the world. Tato is so that you can practically travel around the country without having to leave it, although from a time to this part begins to appear. So while it is not common there are certain places where you should tip, it is not capitalized duty which is acceptable. In what specific situations?
Well, if you move on a tour of China, the usual thing is to leave a tip the bus driver and guide. It was not so common before but there are always tourists who start with the custom and ... you know what happens. It is more a practice of the traveler than of the tourism company, but in this area no one is going to refuse to receive an extra that is given so voluntarily. On the other hand the tip is acceptable in Hong Kong and Macao.
Finally, in high-end restaurants it is also acceptable to leave a tip. If you spend more than one hundred US dollars, it is customary to leave an extra. If you are not in a restaurant this elegant it is not necessary to walk.