Long March-5 Y2 will be fuelled by liquid hydrogen, kerosene and liquid oxygen, Xinhua reported.
China is preparing to launch a powerful rocket on Sunday as the country presses on with its ambitious space program.
Designed to lift space station components, deep-space probes and communication satellites into orbit, the Long March-5 Y2 is Beijing's second heavy-lift rocket able to carry up to 25 tonnes -- or around the same weight as 16 cars.
It will take off from the Wenchang launch center in the tropical island province of Hainan, carrying the new Shijian-18 experimental communications satellite, state broadcaster CGTN reported Saturday.
It said the satellite will operate on geosynchronous orbit and provide communications services over China's territory -- boosting internet access and providing access to more television channels.
The process of filling propellant into fuel tanks began Saturday afternoon, CGTN said.
Xinhua state news agency reported last week that the Long March-5 Y2 will be fuelled by liquid hydrogen, kerosene and liquid oxygen.
Beijing sees its multi-billion-dollar space programme as a symbol of its rise and of the Communist Party's success in turning around the fortunes of the once poverty-stricken nation.
Last month it successfully launched the Long March-4B, its first X-ray space telescope to study black holes, pulsars and gamma-ray bursts.
And in April, the country's first cargo spacecraft completed its docking with an orbiting space lab -- a key development toward China's goal of having its own crewed space station by 2022.