China is buying another eight batteries of Russian S-300PMU2 air defense systems. China received its first four S300 batteries in 1993. The S-300 system is roughly equivalent to the U.S. Patriot system and was known as the SA-10 to NATO, when the system first appeared in the early 1980s. S-300 missiles weigh 1.8 tons each and are 26 feet long and about 20 inches in diameter. The missiles have a range of some 200 kilometers and can hit targets as high as 100,000 feet. The missile has a 320 pound warhead. China has been a major purchaser of S-300 systems, reportedly including over a thousand missiles.
China has a huge air defense force. Like the rest of their armed forces, it's a combination of (mostly) old stuff, with some new equipment. There are about 150 SAM (Surface-to-Air Missile) battalions. However, about half of these are Chinese versions (the HQ-2) of the Russian SA-2 systems from the 1950s. The Chinese have upgraded the SA-2 with modern electronics, an improved warhead, better rocket motors and more maneuverability. The inventory of missiles is believed to be about 10,000. However, many are older models, and many of these are probably of uncertain reliability. American electronic countermeasures can probably defeat all models of the HQ-2. Newer models of the HQ-2 have a range of 40 kilometers, and will hit the target 70 percent of the time (if there are no countermeasures.) The HQ-2 radars have a hard time dealing with stealthy aircraft, and the radar is needed to guide the missile to its target (via radio signals from the ground to the missile).
Another ten percent of Chinese SAMs are based on the French Crotale system. These HQ-7s are short range (up to 15 kilometers) missiles that are very effective against low flying aircraft. The rest of the SAMs are based on the Russian S-300 system (roughly equal to the U.S. Patriot.) Again, there are several versions of these, from early ones that barely match the first Patriot systems, to a few battalions equipped with very formidable missiles. The recent order of S-300s are the latest version.
There are also 30 battalions of anti-aircraft guns (about 50 guns each). These are mainly twin 23mm guns or 57mm guns, plus single 85mm or 100mm guns and some weapons of other calibers. All these are radar controlled. In addition, there is an anti-aircraft "militia" equipped with some 1,500 battalions of guns (that's over 70,000 anti-aircraft guns). The weapons are not in the best shape, and most are quite old. The crews are poorly trained reservists, and they don't get much practice with live ammunition. However, if there were a war, most of these guns would be manned, and better trained, in a few weeks. However, a lot of the ammo reserves are old, so a lot of the shells would be duds.