Based on the result of investigations and former records, there are five freshwater species of the genus Thermocyclops in China, namely T. taihokuensis Harada, 1931, T. crassus (Fischer, 1853), T. vermifer Lindberg, 1935, T. dybowskii (Lande, 1890), and T. kawamurai Kikuchi, 1940. Two previously recorded species, T. brevifurcatus Harada, 1931 and T. hyalinus (Rehberg, 1880) are recognized as synonyms of Thermocyclops crassus. Another species, Thermocyclops mongolicus Kiefer, 1937, described from China by Tai & Chen, is a synonym of T. taihokuensis based on this study. Thermocyclops orientalis Dussart & Fernando, 1985 was compared with Thermocyclops kawamurai Kikuchi, 1940. It shows conspicuous differences and it seems unlikely that it is a synonym of T. kawamurai. The paper presents diagnostic characteristics of each species and a key to five Chinese species of Thermocyclops.