Szuhsiung Ho, aka Allen Ho, helped Chinese efforts to develop nuclear power for almost 20 years, said the US Department of Justice.
Ho was prosecuted because he did not obtain explicit permission to share "sensitive" nuclear technologies.
He was also fined $20,000 (£15,500) for breaking the US tech transfer rules.
Ho, who was born in Taiwan but became a naturalised US citizen, worked as a senior engineer for China's largest nuclear power company and also lead a Delaware-based company called Energy Technology International.
The DoJ said Ho aided China by recruiting engineers and other experts to advise it on faster ways to design and build components for some types of nuclear reactors.
The intellectual and engineering aid he helped funnel toward China helped it reduce costs and cut development time for novel reactor types, said the Justice department.
It also helped with work China was carrying out on fuel assembly systems and sensors to monitor power plant cores.
Many of the technologies involved in using radioactive material to generate power are on a proscribed list, and anyone seeking to share them must first get permission from the US Department of Energy to do so.
"Theft of our nuclear technology by foreign adversaries is of paramount concern to the FBI," said Renae McDermott, the special agent in charge of the investigation, in a statement.
"We will aggressively investigate those who seek to steal our technology for the benefit of foreign governments," she said.
