The U.S. Department of State has announced that F, J, and M multiple-entry visas for Chinese citizens will be valid for up to 5 years starting November 12, 2014. Business visitor visas will be valid for up to 10 years.
Similarly, student and visitor visas for U.S. citizens to China will also be extended.
See more about this change here: https://travel.state.gov/content/visas/english/news/ChinaVisas.html