Do they though? By what metric?
In terms of foreign investment they trail Europe by a VERY large margin. The US also invests more overseas than the combined amount all countries invest in the US.
You might be thinking about debt maybe? China owns "a lot" of US debt. No doubt. However, again, not the most. Japan (yes ... Japan ... the country idiot panic merchants said would own the US in the 80s and 90s and now they never talk about) owns more (very slightly and these are rough estimates but the best we have) than China. Europe has essentially the same amount as China too. It's essentially a three way tie.
China doesn't own more than 25% of US debt and less than 15% of investments.
(Some of this depends on which source you use, how the article might combine debt and investment etc. but there aren't any views that end up with China owning significantly more than Europe or Japan or the US itself. Hell the Federal Reserve and pensions etc. owns more US debt than any foreign entity.)
http://www.cfr.org/content/publications/attachments/images/January15/8 foreign direct investment.png
https://www.washingtonpost.com/news...-shows-which-countries-own-the-most-u-s-debt/
http://money.cnn.com/2015/04/15/news/economy/japan-china-us-debt-treasury/
Aside from the fact they have no real roadmap to develop a real middle class domestic consumption economy (of scale), their slowing growth, their looming construction bubble, and most of their water is poison I'm sure China will have no other hurdles in dominating the world like bores go on about all the time. Remember: nothing happening right now is new. Born in the UK, live in Canada ... no horse in the race other than hating when people fall for the media's agendas. China is likely to be over-estimated for a few more years until it stagnates enough to start being underestimated (because it will still be massive but bells will see their failure to reach levels only their own fevered dumb dumb minds imagined and hold it against them ... like how Japan isn't "supposed" to hold the most US debt it's supposed to be China so everyone can be afraid of Russia/China/Middle East ... Japan and Europe "owning the US" doesn't fit the narrative).