The invention provides a variable-rotation-speed turbine. The variable-rotation-speed turbine comprises a high-and-intermediate-pressure cylinder and a low-pressure cylinder, wherein the high-and-intermediate-pressure cylinder is provided with a first rotor shaft, and the low-pressure cylinder is provided with a second rotor shaft. The variable-rotation-speed turbine further comprises a speed change mechanism. The output end of the speed change mechanism is connected with the first rotor shaft. The input end of the speed change mechanism is connected with the second rotor shaft. When the operation backpressure of the turbine rises, the steam enthalpy drop delta h of the low-pressure cylinder is reduced, and the speed change mechanism is used for reducing the rotation speed n of the second rotor shaft of the low-pressure cylinder. When the operation backpressure of the turbine lowers, the steam enthalpy drop delta h of the low-pressure cylinder is increased, and the speed change mechanism is used for increasing the rotation speed n of the second rotor shaft of the low-pressure cylinder. According to the variable-rotation-speed turbine, the rotation speed of the low-pressure cylinder of the turbine is changed through the speed change mechanism, the variation of the rotation speed of the low-pressure cylinder corresponds to the enthalpy drop variation, generated when the operation backpressure of the turbine changes, of the low-pressure cylinder, and therefore the speed ratio of the low-pressure cylinder is always within a reasonable design range; and in this way, safe operation of the turbine set is guaranteed, and the economical efficiency of the turbine set is also improved.