The constant failure rate played a fundamental role in reliability analysis for the protection devices. This paper focused on the computation approaches for the constant failure rate with the field data. It first listed the evaluation methods

which are the maximum likelihood estimation (MLE) and least square estimation with linear fitting (LSF)

for the constant failure rate according to the natural of the field data. In detail

it deduced the MLE (point estimation and interval estimation) with the censored data and incomplete data. Finally

the estimation of the constant failure rate for the protection equipment of a power system with the field data was carried out

and the difference of the estimation approaches are compared. The results indicated that it was important to take data censor problem into consideration when we calculated constant failure rate with field data. Further

the adaptability for different methods with different data types were also analyzed.