|Type||Intercontinental ballistic missile|
|Place of origin||People's Republic of China|
|In service||2006 (DF-31), 2007 (DF-31A), in development (DF-31B)|
|Used by||Second Artillery Corps|
|Manufacturer||Academy of Rocket Motors Technology (ARMT)|
|Weight||42 t (41 long tons; 46 short tons)|
|Length||13 m (42 ft 8 in)|
|Diameter||2.25 m (7 ft 5 in)|
|Warhead||1 Thermonuclear weapon@ 1 Mt or 3 Nuclear (DF-31A) @ 20, 90, or 150 kt each with MaRVs|
|7,200–8,000 km (4,500–5,000 mi) (DF-31)
11,200 km (7,000 mi) (DF-31A)
|Astro-inertial guidance with BeiDou Navigation Satellite System|
|Silo, 8 axle TEL|
The Dong Feng 31 (Chinese: 东风31; literally: "East Wind 31"; NATO reporting name CSS-9) is a long-range, road-mobile, three stage, Solid-fuel rocket intercontinental ballistic missile (ICBM) in the Dongfeng missile series developed by the People's Republic of China. It is designed to carry a single 1-megaton thermonuclear weapon. It is a land-based variant of the submarine-launched JL-2. It is operated by the Second Artillery Corps (SAC) which, in 2009, was estimated to have under 15 DF-31 missiles and under 15 DF-31A missiles in inventory. It is not known how many missiles of this type the SAC currently has.
The DF-31A is believed[who?] to have incorporated many advanced technologies similar to current generation Russian ICBMs, including the use of penetration aids such as decoys or chaff and maneuverable reentry vehicles to complicate enemy's missile warning and defense system.
The PRC began developing the DF-31 as a second-generation ICBM successor of the DF-4 in January 1985. ARMT (then called the 4th Aerospace Academy) was appointed as the main contractor while the research arm of the Second Artillery Corps provided contributing support. The land-based variant of the JL-2 was originally called the DF-23 but was changed later on to the DF-31 because of a change in operational requirements. In 1999, the missile was first displayed publicly at the National Day Parade. On August 2, 1999, the Chinese state news media reported the successful test of the DF-31. The third test flight of the missile occurred on November 4, 2000; the second test flight had taken place earlier that year.  Operational deployment of the missiles reportedly began in 2006. In 2009, US Air Force Intelligence reported that under 15 DF-31 missiles had been deployed.
The PRC has developed an improved variant of the DF-31 called the DF-31A. This upgraded missile has a reported range of 11,200 km, and possibly MIRV capability to hold 3 warheads each capable of a 20–150 kt yield, and penetration and decoy aids to complicate missile defense efforts. The missile was shown to the public during the parade in Beijing celebrating 70 years since the end of World War II on September 3, 2015. It can carry maneuverable reentry vehicles.
The PRC is developing another improved variant of the DF-31 called the DF-31B with the purpose of improvement in comparison to the DF-31A. China has successfully tested it from a mobile launcher.
- CSS-9 (DF-31), missilethreat.com
- Annual Report to Congress: Military Power of the People's Republic of China 2008, Office of the Secretary of Defense
- US Air Force Air and Space Intelligence Center, Ballistic and Cruise Missile Threats 2009 
- Diamond, Howard (July 1, 1999). Arms Control Today (Arms Control Association). ISSN 0196-125X http://www.highbeam.com/doc/1P3-45738834.html. Retrieved August 22, 2015 – via HighBeam Research. (subscription required (. )) Missing or empty
- The Federation of American Scientists & The Natural Resources Defense Council (DF-31A) Nov, 2006. 73 (PDF)
- Gertz, Bill (December 13, 2000). "Pentagon Confirms China's Missile Test". The Washington Times. Retrieved August 22, 2015 – via HighBeam Research. (subscription required (. ))
- Minnie Chan (23 January 2014). "China's nuclear missile drill seen as warning to US not to meddle in region". South China Morning Post. Retrieved 24 January 2014.
- Minnie Chan (4 October 2014). "China puts on show of force with DF-31B mobile ICBM missile test". South China Morning Post. Retrieved 10 October 2014.
- China tests 10000 km nuclear missile 4. October 2014
- "China has successfully test-launch of DF-31B intercontinental ballistic missile from mobile launcher 19. March 2015
- Giacometti, Nicolas (10 April 2014). "China’s Nuclear Modernization and the End of Nuclear Opacity". thediplomat.com. Retrieved 12 April 2014.