Human Rights Watch says women are often tricked into traveling to China in search of work or kidnapped and held against their will to be sold as "brides" for Chinese men.
The report says the 226 known cases of such trafficking in 2017 were only a fraction of the total number.
It says the 37 survivors of such crimes interviewed for the report were sold for the equivalent of $3,000-$13,000.
The group said Myanmar provides help to 100-200 such victims who manage to escape each year. Those taken hostage by Chinese families are often locked up and raped.