Abstract: Under the ultra-low load condition, the temperature distribution in the low pressure cylinder has the direct influence to the safety of steam turbine. In order to study the distribution of temperature field of the whole low pressure cylinder, the numerical simulation was used to calculate the flow field of low pressure cylinder in this paper by the non- equilibrium condensation flow model and SST k-ω turbulence model. The characteristics of flow field, power output, temperature distribution and the influence of cooling steam parameters on the temperature field at near zero power condition of low pressure cylinder were analyzed. Results show that there is a back flow vortex at the diffuser at 30% turbine heat acceptance (THA) condition. The tip clearance vortex appears at the upper span between the last stator blade and the last rotor blade at 20% THA condition and the temperature increases significantly, which is called the "windage" phenomenon and the last stage produces a negative power output contribution. At near zero power conditions, the exhaust temperature of low pressure cylinder is linear with the flow rate and the temperature of cooling steam. It is negatively related to the cooling steam flow rate and positively correlated with the cooling steam temperature. Therefore, the outlet temperature of the last two stage blades can be effectively controlled by setting the cooling steam flow rate and temperature reasonably. The research results can provide reference for the operation of steam turbine under ultra-low load conditions.