Abstract: In this paper,the reliability method and model of CETRM（Constant Electrical stress and Temperature Ramp stress Method）is introduced in detail.Based on the degenerate graph of input current, output current and output voltage in DC/DC converter,the reliability life method is researched and the life in the normal working conditions which was reckoned is about 8.7×10⁴ h.In accordance with the degenerate graph,the failure sensitive parameter is output voltage.Then the failure mechanism consistent temperature range is 75℃～160℃by the failure mechanism consistent model.The failure activation energies calculated in this temperature range is 0.59eV.And finally,the life in the normal working conditions is worked out.It proves that the CETRM can be applied in the quantitative evaluation of the reliability in DC/DC converter.