The invention discloses a temperature control system for a hydroelectric generator. The temperature control system structurally comprises a connecting rotation shaft, an electric energy reserve and transmission box, an operating case, heat emission holes, electric energy conversion box, a fixed base, a support frame, set screws, a water outlet and an operating box, wherein a connecting rotation device is connected with a transmission gear set, a pushing gear set is arranged below the transmission gear set, a water outlet channel is embedded in a water flow channel, a main rotating shaft is inthreaded connection with a pushing gear wheel to make contact with an eleventh gear and enable the eleventh gear to rotate, so that an eleventh rotating shaft is driven to operate in an inner rotatingshaft under transmission of a fifth transmission belt, the inner rotating shaft drives an outer rotating shaft to rotate, a tenth rotating shaft is driven by a fourth transmission belt, then a tenthgear is driven to make contact with the main rotating shaft and control rotating speed of the main rotating shaft, the hydroelectric generator is enabled to slow down, and friction force is reduced; the hydroelectric generator can slow down by multiple transmission groups when rotating at high speed, and temperature of the hydroelectric generator is reduced by reducing friction force of the hydroelectric generator.