Abstract: The mechanical properties of the closed impeller assembly in a heavy-duty turbine compressor was investigated under actual operating conditions. Based on FEM and nonlinear contact theory, the size and distribution of stress of the assembly were analyzed structurally in assembling process and under variable operating conditions. The results showed that the assembly cannot fail structurally due to the internal stress caused during its assembling. There are stable and non-stable operating regions of a closed impeller assembly and most of those assemblies will malfunction structurally if they work at a speed over 12?000?r/min. The analysis method proposed is highly practical in applications as a reference for the study on mechanical properties of other rotor assemblies.