The effect of the number of blades and load application on the reliability of turbine impeller was studied, and the reliability and failure rate models of turbine impeller of turbocharger under ultimate load were developed. The structural characteristics of turbine impeller were analyzed, and the probability distribution function of strength of turbine impeller capable of reflecting the effect of the number of blades was derived. For the failure mode caused by the ultimate load of over speed, the models of reliability, failure rate and mean life of turbine impeller were developed, which could embody the effect of the number of blades, load, strength and the operating cycles. Taking a turbocharger as an example, the behavior of the reliability and failure rate of turbine impeller changing as the number of operating cycles was studied. The results showed that as the number of operating cycle increased, the reliability of turbine impeller decreased, and the failure rate also decreased and approached to a stable value. Compared with the conventional methods, the models proposed can be applied to analyze and calculate the reliability of turbine impeller more scientifically.