Abstract: We discuss the problems about lifetime testing in this paper by four parts. In the first part we point out the difficulties that we may meet in the lifetime testing. In the second part the estimations of the lifetime in non-parametric model under nodified type Ⅰ censoring are considered while the estimations of mean lifetime under random censorship model are given based on the Kaplan-Meier estimator in the third part. In the last part we study how to determine the r value of the type Ⅱ censoring to save the money and the time.