President Xi once called President Putin his "best friend". The two have much in common: they are both authoritarian leaders, and both embrace the idea of a "multi-polar world" devoid of US domination.
In Moscow they're expected to sign an agreement on "deepening the comprehensive partnership" between their two countries.
The Chinese president's state visit is a clear sign of support for Russia - and its president - at a time when the Kremlin is under intense international pressure.
And Russia's relationship with China is fundamental to withstanding that.
"Putin is building his own bloc. He doesn't trust the West anymore - and he never will again," believes journalist Dmitry Muratov, a Nobel Peace Prize laureate.
"So, Putin's looking for allies and trying to make Russia part of a common fortress with China, as well as with India, some parts of Latin America and Africa. Putin is building his anti-Western world."
In this "anti-Western world", Moscow is heavily reliant on Beijing - now more than ever, as the war rages in Ukraine.
"War has become the organising principle of Russian domestic politics, foreign policy and economic policy. There is an obsession with destroying Ukraine," concludes Alexander Gabuev, a senior fellow at the Carnegie Endowment for International Peace.
"For that you need arms, money and an economic lifeline. China provides Russia with, at least, components for arms, and civilian technology that can be used for military purposes. It definitely provides money."
To counter Western sanctions, and to shore up the Russian economy, Russia has been boosting trade with China, primarily in the energy sector. Expect oil, gas and energy pipelines to be on the agenda at the Putin-Xi talks.
But, once again, imagine you're Putin. One year ago you and Xi proclaimed that your partnership has "no limits". If that's really the case, might you expect China now to help you out in Ukraine, by supplying Russia with lethal aid and facilitating a military victory for Moscow? The US claims that China is considering doing just that. Beijing denies it.
As they say in Russia, "there's no harm wishing for something" - but it doesn't mean it's going to happen. If there's one thing the last year has shown it is that the "no-limits partnership" does have limits. Up to this point Beijing has apparently been reluctant to provide direct military assistance to Moscow, for fear of triggering secondary sanctions in the West against Chinese companies. As far as Beijing is concerned: sorry Russia… it's China first.
That very point was made very bluntly recently on a Russian state TV talk show.
"Ahead of President Xi's visit to Moscow, some experts here have been overexcited, elated even," noted military pundit Mikhail Khodarenok.
"But China can have only one ally: China itself. China can only have one set of interests: pro-Chinese ones. Chinese foreign policy is utterly devoid of altruism."