The invention discloses an open and closed type combined technical water supply system for a hydropower station, and belongs to the field of water supply systems in the hydropower station technology. The system comprises an open type water supply device, a closed type water supply device, a first operation valve bank and a second operation valve bank. One end of the open type water supply device is connected with a water source, one path of the other end of the open type water supply device is sequentially connected with the first operation valve bank, a cooling object, the second operation valve bank and hydropower station tail water or hydropower station downstream, and the other path of the other end of the open type water supply device is connected with the closed type water supply device and the hydropower station tail water or the hydropower station downstream in series. The closed type water supply device and the cooling object are connected to from a circulation loop. The system is applicable to hydropower stations with water quality of water supply sources obviously changed along with seasons, can remarkably improve the reliability of water supply of the hydropower station technology, and reduces the operation cost. Besides, the system is provided with a work branch and a standby branch which can be switched, the whole system is convenient to overhaul, and the reliability of the system is further improved.