The line connecting Hefei, the capital of Anhui Province, and Shanghai, a coastal trade hub, has 11 trusted nodes along its length, Xinhua news agency reported on Sunday.
It transmitted a secure video conference between the two cities in one of its first test communications.
The line, already three years in the making and yet to be finished, will ultimately connect Shanghai to China's capital, Beijing, and run through another major city, Jinan, with a total of 32 relay points. The entire project was expected to be finished in November, but the completion date has been moved back until at least the end of the year.
Quantum communication uses quantum entanglement of photons to ensure that nobody taps into the line, as doing so would inevitably corrupt the signal. The relay nodes are weak points, because the information is translated back into regular form there before being re-entangled and sent further along the optic fiber link.
The Chinese network is valuable for both research on how the technology can be used, and practical purposes, such as delivering secure messages between the connected cities.