China's economic growth slowed down to 7.4 per cent year-on-year in the third quarter of 2012, slower from 7.6 percent in the second quarter and 8.1 percent in the first, the National Bureau of Statistics (NBS) said.Industrial value-added output grew 10 per cent in the first nine months of the year, 0.5 percentage point lower than growth in the first six months of 2012.