Hi Jerry,
Yes the Chinese government has exchange controls in place to prevent speculation in the Yuan. It is not impossible to trade it however, institutions trade it through the over the counter forwards market which is basically a derivative of the spot forex market which you are trading now.
Two places where individuals can trade the Yuan that I know of are
OANDA, The Currency Site: Foreign Exchange Services and Trading and in the futures market. The problem with trading the Yuan with Oanda is since the currency is not liquid the spreads are 60 points or wider and you could theoretically get caught in a position, not a situation which most traders want to be in. Same goes for the futures there is not a lot of liquidity so unless you are looking for a longer term bet then I would stay away.
Hope that helps.
Best Regards,
Dave