Fixed-asset investment, an important driver of economic activity, grew 16.5 percent in the first eight months from the same period last year, also lower than forecast, it said.
Retail sales climbed 11.9 percent.
Economists polled by Reuters had forecast industrial output to rise 8.8 percent and retail sales to rise 12.1 percent. Fixed-asset investment for the January-August period was seen up 16.9 percent.
Output grew 9.0 percent in July and retail sales 12.2 percent, with Jan-July fixed-asset investment up 17.0 percent from the same period a year earlier.
China's economy got off to a weak start this year as first-quarter growth cooled to an 18-month low of 7.4 percent. A raft of government stimulus measures pushed that up slightly to 7.5 percent in the second quarter, but recent data have suggested the economy may once again be losing momentum as a cooling property market weighs on other sectors.
The government has pledged to maintain targeted policy measures to help achieve its annual economic growth target of 7.5 percent.