The reliability of image sensors, as core components of remote-sensing payloads, directly determines the overall lifespan of remote-sensing satellites. CMOS image sensors have become the primary visible-light detectors for remote-sensing payloads. However, the existing lifetime - evaluation methods rely primarily on quality-assurance tests, which are devoid of quantitative analysis. This study proposes a mission requirement-based lifetime-evaluation method for space-applied CMOS image sensors. Based on a virtual remote-sensing satellite mission as a case study, a reliability analysis of the device (including failure mechanisms such as the time-dependent dielectric breakdown (TDDB)) was conducted at the design stage, and a quality-assurance scheme was formulated during the test phase. Through irradiation experiments focusing on the performance degradation caused by the total ionizing dose, displacement damage, and TDDB effects as well as predictions of cumulative irradiation levels in the mission environment, key indicators such as the imaging signal-to-noise ratio (SNR) of the CMOS image sensor at the end of the camera's lifespan were quantitatively evaluated. Experimental results indicate that the performance degradation of the device remains controllable within the 8-year design lifetime, with the SNR satisfying the mission requirements. This method provides theoretical support for the reliability design and verification of long-life remote-sensing cameras.