US Defence Secretary Robert Gates has visited China's nuclear warfare headquarters.
"There was a discussion of nuclear strategy," including China's policy of not using nuclear weapons pre-emptively, Mr Gates said.
Officials from both countries praised the four-day visit as a success.
Beijing froze military ties last year because of an arms sales to Taiwan by the United States.
The rare view of China's nuclear and missile arsenal was given on a trip to the Second Artillery Corps of the People's Liberation Army headquarters.
The BBC reports that both the US and China have long-range missiles capable of reaching each other's shores, but both have said they do not intend to use them.
Mr Gates said the commander of the nuclear headquarters, General Jing Zhiyuan, has accepted an invitation to visit the US Strategic Command headquarters in Nebraska.
"I think the discussions were very productive and set the stage for taking the military-to-military relationship to the next level," he said.
President Hu Jintao of China is to visit Washington next week. China has agreed to more direct military co-operation with the US, but the BBC reports it remains unclear how open and collegial such exchanges will be.