http://devdata.worldbank.org/data-query/
the GDP figures are calculated on a exchange rate conversion to US$ for comparison. The figures you presented were calculated using Purchasing Power Parity which for a developing country gives rough approximations but still a useful comparison tool none the less. The 1.7 trillion is the expected figure for this year (that is with 9% annual growth rate in GDP). The worldbank shows GDP for China in 2003 was 1.4 trillion.