An economic slowdown will make it harder for China to revive the borrowers as some projects they did with help of a past huge stimulus program were not commercially viable, it added.
S&P, which surveyed the 200 biggest corporations by revenue and bond issuance, said financial risks for many companies will likely intensify as China's economy slows.
The most vulnerable to a sharp downturn are asset-heavy ones and capital-intensive sectors, it said.
The survey accounted for 20 percent of the non-financial corporate debt in the world's second-largest economy at the end of 2013, equivalent to 30 percent of GDP. Companies were in 18 industries.
"The baseline assumption is that the next 12 months could see an acceleration of corporate stress. The deteriorating trend is still there in almost all industries," Christopher Lee, S&P credit analyst and co-author of the report, told Reuters.
Timely, incisive articles delivered directly to your inbox.