I didn't explain myself clearly: if China had a comparable GDP per capita as Japan, its GDP would be 3.5x bigger than that of US. But currently China GDP per ca

I didn't explain myself clearly: if China had a comparable GDP per capita as Japan, its GDP would be 3.5x bigger than that of US. But currently China GDP per capita is 10x smaller than that of Japan ($3600 vs $37500). $130B times ten would bring China defense budget to a staggering $1300B. $1300B is quite a bit more than $600B, but indeed not 3.5x more. Two factors are at play: US defense budget is larger in scope than that of China (for instance, if I remember correctly, most rocketry stuff fall under defense budget in US, but not in China), and China just doesn't spend as much (as a percentage of GDP) as US for its defense. Again, China has a very very long way to go.