China's imports in August fell 14.3% in yuan-denominated terms from a year ago, while exports fell by 6.1%.
The steep fall in the value of imports reflects lower commodity prices globally, particularly crude oil.
The numbers mean China's monthly trade surplus expanded by close to 40% from the month earlier to 368bn yuan ($57.8bn; £37.7bn).
China recently revised down its 2014 economic growth from 7.4% to 7.3%, its weakest for almost 25 years.
In US dollar denominated terms, exports for the month of August fell 5.5% from a year earlier - slightly less than expected - while imports fell by 13.8%, leaving China with a surplus of $60.24bn.
Currency conversion factors based on US dollar and Chinese yuan movements over the last year mean some official numbers from the mainland are now reported in both currencies.
A fall in both import and export figures had been expected as China's economy slows, though analysts said the drop in imports was greater than forecast.
"Chinese investors are now poised to expect a slew of weak economic data ranging from foreign trade to PMI [purchasing manager's index] to industrial output," said Xiao Shijun, an analyst at Guodo Securities in Beijing.
But he said investors were "no longer nervous about relatively poor figures. So unless there are fresh surprises on the downside, market impact will be limited".