Due to arrive in the early afternoon, Xi will be received with full honours.
He will have talks in the Kremlin with President Vladimir Putin before attending a formal reception and in the evening he will attend a night out at the Bolshoi theatre.
The visit comes five years after Moscow's annexation of Crimea in 2014 led to a serious rift with its Western partners and subsequent turn toward its neighbour to the east.
From Moscow, Xi will travel to Russia's former imperial capital Saint Petersburg to attend the Economic Forum hosted by Putin on Thursday and Friday.
China and Russia "have strong political mutual trust and support each other firmly on issues concerning each other's core interests and major concerns," Xi said during an interview with Russian media ahead of the visit, according to a transcript released by Beijing's official Xinhua news agency.
Putin's foreign policy aide Yury Ushakov said the visit is "a crucial event for our bilateral relations". The Soviet Union was the first country to recognise Communist-ruled China in 1949, he remarked.
He said Xi and Putin would sign a new declaration on "global partnership and strategic cooperation, which enter a new era".
The Chinese delegation is bringing two pandas as gifts, which are bound for the Moscow Zoo. "The animal is a symbol of China and the gesture is very important to our partners," Ushakov said.
The partnership is yielding increasing trade, which has increased by 25 percent in 2018 to hit a record $108 billion, he said, calling China "Russia's most important economic partner".
Chinese Vice Foreign Minister Zhang Hanhui praised the upcoming visit as having a "milestone significance in the development of bilateral relations".
Russia's 'pivot' paying off
Russia may have had unrealistic expectations from its pivot to the east following Western sanctions over Ukraine, said Alexander Gabuev, who heads the Asia programme at the Carnegie Moscow Center.
Nevertheless, China's share in Russian foreign trade has nearly doubled since then, he added.
"The pivot really is happening," he said.
"Despite all the difficulties, China became a significant creditor and rather significant investor" in Russia at a time when many other investors preferred to pack their bags.
For Russia, whose alternative for economic growth is launching deep reforms and reconciling with the West, gradually increasing dependence on China "is perceived as the lesser of two evils", said Gabuev -- provided it did not reach critical levels.
Politically, the two countries seem consistently aligned and often vote in unison as permanent members of the UN Security Council.
"The positions of Russia and China are very close or coincide completely on most international issues," including the North Korean nuclear programme, the Venezuelan crisis and the Iran nuclear deal, Ushakov said, adding that all these issues would be discussed during the talks.
Both countries would also discuss their relationship with the "great Western powers, including the United States", he said.
Moscow's relations with Washington have been at a post-Cold War low for some time now, and Beijing is locked in a trade war with the US.
And after Washington criticised its rights record, Beijing issued a travel warning to Chinese nationals Tuesday about crime and police harassment in the United States.