The invention relates to a steam turbine, in particular to a steam-coagulating back-pressure steam turbine, and aims to solve the problems that existing extraction condensing steam turbines for heat supply units have limited heating capacity, and back-pressure steam turbines cannot provide more heating quantity for discontinuous heating due to structural limitation, especially in extremely cold working conditions in winter, and are poor in applicability. The steam-coagulating back-pressure steam turbine comprises a high-intermediate-pressure combined cylinder, a low-pressure cylinder, a first bearing box, a second bearing box, a third bearing box, a clutch, a high-intermediate-pressure rotor, a low-pressure rotor, an intermediate shaft, two low-pressure valves, two low-pressure steam guide pipes, two intermediate-low-pressure steam guide pipes and two switch valves. The high-intermediate-pressure combined cylinder is arranged between and connected with the first bearing box and the second bearing box. The second bearing box is arranged between and connected with the high-intermediate-pressure combined cylinder and the low-pressure cylinder. The third bearing box is arranged at the other end, opposite to the low-pressure cylinder, of the second bearing box. The intermediate shaft and the clutch are arranged between the high-intermediate-pressure rotor and the low-pressure rotor. The steam-coagulating back-pressure steam turbine is applied to heat supply and power generation of combined heat and power generation.