The invention discloses a double-working medium cooling heat supplying system and method suitable for three-steam discharge type turbosets. According to the characteristics of a large quantity of in-operation three-steam discharge type turbosets in China, the efficient and flexible double-working medium cooling heat supplying system suitable for the turbosets is developed. In the system heat supply period, double-working medium cooling running is adopted, one cooling working medium is circulating cooling water, the other cooling working medium is heat supply network circulating water, a powerplant can flexibly select different steam exhaust port high backpressure and low backpressure running modes according to the actual condition of the self heat network circulating water amount, the problem that the heat network circulating water amount in most power plants is insufficient and consequently high backpressure heat supply running can be caused is solved, the unit heat supply capacity and the heat supply economical efficiency are obviously improved on the basis of middle and low pressure communication pipe steam exhausting, and meanwhile, the heat supply system further has a certainrunning flexibility.