Pranee Sutthasri, senior director of the central bank's macroeconomic department, said the projection for total foreign arrivals has also been revised down from 39.5 million to 37.5 million, Bangkok Post newspaper reported.
Last year Thailand received over 35 million visitors, including 6.7 million Chinese.
Only 1.83 million Chinese had visited by May 18.
Safety concerns have weighed on the minds of Chinese following the high-profile kidnapping of Chinese actor Xing Xing in January.