Large-scale synthesis of single-crystal CdS microbelts was achieved by a modified thermal evaporation method, in which an adiabatic layer was used to provide abrupt temperature decrease and high gas concentration for the microbelt growth. The synthesized CdS microbelts were usually several micrometers in width, 70 nm in thickness, and tens to several hundred micrometers in length. Studies found that the adiabatic layer has great influence on the formation of CdS microbelts. Room-temperature photoluminescence indicated the disappearance of the emission at 1.77 eV, the appearance of an emission at 2.07 eV, and also the enhancement of the emission band at 2.38 eV, whose position shifted toward the blue region compared with conventional narrow CdS nanobelts. A possible growth mechanism of the CdS microbelts was briefly discussed.