This study explores the effect of the recently enacted Foreigners' Working Management Emergency Decree, 2017 on migrant insurance coverage between January 2016 and December 2018. We employed an interrupted time series (ITS) model to estimate the level and trend changes of the number of migrants enrolled in Social Health Insurance (SHI) for formal workers and the Health Insurance Card Scheme (HICS) for other migrants. Before the Decree's implementation, SHI covered roughly a third of the total migrants holding work permits, while HICS covered over half of migrants in the country. We found that the new employment law contributed to a rise in the volume of SHI members and a decline in the HICS members in the long run, which might be partly due to a switch from the HICS members in the formal sector to the SHI, as originally intended by the law. In addition to the law effect, some coincided political force from international trade partners and supranational organizations might also contribute to the progress in protecting the rights of migrant workers. The long-term monitoring of migrant insurance coverage and a mapping against the changes in migrant-related laws and contexts are recommended.