A device and method for measuring an upper energy level lifetime of a CO2 laser amplifier (20). The device comprises: a signal trigger (10) used to send a trigger signal to a CO2 laser amplifier (20) under measurement so as to activate the CO2 laser amplifier (20) to excite operating particles to transition into an upper energy level; and a measurement device (30) used to perform measurement and analysis on transition-generated light generated by energy released from a transition of the operating particles from the upper energy level to a lower energy level, and to determine, according to energy of the transition-generated light and a duration, an upper energy level lifetime of the CO2 laser amplifier (20). In the invention, a CO2 laser amplifier (20) is used to excite operating particles, and measurement is performed on transition-generated light to obtain an upper energy level lifetime, such that an actual operating process of the CO2 laser amplifier (20) can be more realistically simulated, thereby obtaining a more accurate upper energy level lifetime, and providing a reliable data-based foundation for applications of the CO2 laser amplifier (20).