The transmissivity of optics is one of the important properties for high power output of laser system.This paper proposes a new method to measure transmissivity of large aperture otpics of the ICF system.A measurement system is constructed,and its accuracy and repeatability are analyzed by the cavity measurement for 10 times.The experimental results show that the transmissivity accuracy of the system is 0.1%,and the repeatability is better than 0.08%.In the other hand,large aperture optics with and without ...