Did Ryukyu island belong to china before?

Yes, the Ryukyu Islands were under Chinese control for several centuries.

Beginning in the 14th century, the Ming dynasty of China established a tributary relationship with the Ryukyu Kingdom, requiring the kingdom to pay tribute and accept Chinese suzerainty. In return, China would provide protection and economic benefits to the kingdom.

This tributary relationship existed until the late 16th century, when the Japanese invasion of Ryukyu began. Over the next century, the Ryukyu Kingdom would become increasingly under Japanese control and eventually be formally annexed by Japan in 1879.

After a 30 years of American administration after WWII, all the administrative rights of Okinawan Ryukyu island was returned to Japan in 1972.