Who would win in a war between Russia and China?

It would be a close fight. China has more men to fight with. China also has more reserves. China has unquestionably better navies and air forces when compared to Russia, and around 9 times the amounts of tanks. China has the largest army in human history, more than the entire population of the United States. So, in a short war, China would win. In a longer war, China would win and begin to take Russian lands, eventually scoring the victory.

This is of course assuming no nuclear weapons are used. Otherwise, China would also win.

Answer:

China would win without really trying.