Chinese currency is used almost exclusively in Shenzhen. Many guidebooks will tell you that you can use Hong Kong Dollars in Shenzhen. Be wary of this advice, as it is now out of date. Twenty years ago it was true. It is still true in those places such as the Luohu Commercial City, which cater mainly to Hong Kong shoppers, although the rate of exchange offered may be unfavourable. Outside these areas it is far from true, and it is becoming increasingly less so as the Hong Kong Dollar depreciates against the Yuan. Now, most places will not accept Hong Kong Dollars and taxi drivers will try to unload their Hong Kong Dollars at one for one, a discount, on unwary travellers.
The Chinese currency is called the Renmin Bi RMB or People’s Currency. The denomination is the Yuan $, divided into ten Jiao colloquially called Mao, which are in turn divided into 10 fen or cents. People often won’t bother with smaller denominations. Taxi drivers routinely round up or down fares to the nearest Yuan.
The Yuan comes in notes of $100, $50, $20, $10, $5, $2, $1, and 5 Jiao. Additionally there are coins of $1 and 5 and 1 Jiao.
Incidentally in Chinese Yuan is written with the same character, which translates to Dollar in Hong Kong and Malaysia-Singapore, Yen in Japan and Won in Korea. All of these currencies originated with the Mexican Dollar in silver, the standard currency of trade in the 18th and 19th centuries. In Chinese it was referred to as the Yang Yuan Bi or foreign round coin that was shortened to Yuan or round.
Taxi drivers occasionally do not have change for large notes such as $100 so it is a good idea to carry around some smaller notes in your wallet.