This paper dedicates on the rotor dynamics behavior analysis on a tilting pad bearing supported turbo-expander rotor system considering temperature gradient. Both numerical and experimental investigations are conducted intensively. The influence of the temperature gradient is modeled as the change of the lubrication oil viscosity and the length variation of the clearance due to the cryogenic thermal expansion of the journal. The analytical expressions of the tilting pad bearing oil-film force are then amended and substitute into the lumped parameter model of the turbo-expander rotor dynamics. Linear analysis based on this model indicates that the existence of the temperature gradient can stabilize the turbo-expander rotor system to an extent, while the nonlinear analyses reveal that the temperature gradient will advance the occurrence of the quasi-periodic motion and break the equilibrium of the vibration between the expander side and the compressor side. Furthermore, an experimental system is established and the experimental results show that the temperature of the tilting pad bearing is influenced by the environment temperature greatly; the spectrum of the displacement of the rotor is dominated by the synchronous frequency of the impellers and bearings. The experiment results also observe the vibration amplitude decreases when the environment temperature gets down and grows when the rotating speed increases. At the same time, the sensitivity of the vibration amplitude versus rotating speed decreases as the environment temperature rises, and vice versa.