Data retention characteristics and a failure mechanism of TaN/CuxO/Cu resistive memory device are investigated by a temperature-accelerated test method. Data retention capability at 85 degrees C is sufficiently longer than 10 years by using two different methods: simple extrapolation and Arrhenius equation. The high resistance state fails to low resistance state and low resistance state fails to high resistance state at the elevated temperature. It is attributed that different retention-failure mechanisms are responsible for high resistance state and low resistance state, respectively. A filament/charge trapped combined model is presented to clarify the retention-failure mechanism.