Since 1949, when Communist China came to be, the navy has been organized into three fleets; Northern. Eastern and Southern. Back then the Chinese navy was a coastal defense force. For thousands of years China has been content to have little more than a coast guard, mainly to deal with pirates and smugglers. On only a few occasions was there a high seas (or "blue water") fleet.
Since the 1980s China has become a major importer and exporter and, to protect its growing overseas trade, something China has never had before, needs a blue water navy to protect that trade. Such a navy requires not just experienced sailors but support ships. These are the tankers, supply, and maintenance ships that can keep warships operational when they are far from China. In the 1990s China began investing heavily in these ships and by 2021 had the largest fleet in the world and expected to increase the size of their fleet nearly 30 percent by the end of the decade while the Americans were having problems maintaining the force that China just passed in terms of number of warships, but not yet in total tonnage.
China still has some more fundamental naval needs. For example, China has never demonstrated any talent or enthusiasm for anti-submarine warfare. Considering the number of nuclear and conventional subs arrayed against it, anti-submarine warfare should have higher priority in China. Another serious shortcoming is mine-clearing capability. The Chinese Navy is well equipped to plant mines off hostile shores and in defense of its own waters but there is not a lot of capability to clear enemy mines. Many navies share this shortcoming but for a major maritime trading nation like China, it would be sad to see all that trade shut down by a few hundred naval mines.
China is still addressing the ASM (anti-submarine warfare) and mine-clearing but has a modern fleet. The three fleets are equipped with modern ships and the composition of each of the three fleets reflect current needs, including dealing with mine clearing and ASM as well as the nearest naval threats. Each fleet has over a hundred aircraft for ASM, recon and fighters for air superiority and bombers carrying anti-ship missiles.
For example, the Northern Fleet faces Korea and southern Japan. It currently has 66 warships, including an aircraft carrier, 18 attack submarines (four of them nuclear powered SSNs and the rest diesel-electric), 13 destroyers, two of the larger ones classified as cruisers, 12 frigates, 12 corvettes (small frigates) and 15 fast patrol boats armed with anti-ship missiles. There are also five amphibious ships that can carry and land tanks and other vehicles onto a beach.
The Eastern Fleet faces the East China Sea and Taiwan. It has over 140 ships including 18 diesel-electric submarines, 13 destroyers, 23 frigates, 24 corvettes and 38 fast patrol boats armed with anti-ship missiles. There are also 24 amphibious ships that can carry and land tanks and other vehicles onto a beach and three larger amphibious ships with a flight deck.
The Southern Fleet faces Taiwan and the South China Sea. It has about 110 warships including an aircraft carrier and a new base for carriers and subs. There are 22 submarines including 14 diesel-electric and two SSNs. There are also six SSBN (nuclear powered ballistic missile) subs. There are ten destroyers, 14 frigates, 20 corvettes and 14 fast patrol boats armed with anti-ship missiles. There are also 15 amphibious ships that can carry and land tanks and other vehicles onto a beach and five larger amphibious ships with a flight deck.
The Northern Fleet must deal with the two largest and most formidable fleets in the region; South Korea and Japan.
The Eastern Fleet has the longest coastline to defend and the new coast guard comes in handy to help, often using retired and repurposed corvettes. The Eastern Fleet also must assist in the Northern Fleet against South Korea and Japan as well as any attack on Taiwan.
The Southern Fleet is currently concentrating on the South China Sea, as well as contributing forces for any attack on Taiwan.