How to calculate constant GDP in international $ from nominal GDP in local currency units
You need to use PPP rates. These convert basket of goods in one country (in LCU) to that of (normally) the US, in US dollars. You can find these rates here or here. With these rates you can transform nominal GDP in Yuan into nominal GDP in USD. Then, you can use a US CPI or GDP deflator index to transform these nominal international dollars into constant international dollars. The base year is given by the price index you use. 

You can rear more about PPP and how to use it here. 

Finally, in case you do not want to bother to calculate this yourself, or that you want to confirm your calculations, here is the actual series of China's GDP in 2011 international dollars.