Abstract: In order to improve the uniformity of fiber optically coupled intensified CCD(ICCD),its mechanism of formafion is analyzed.A graphic method is adopted to demonstrate how the non-uniformity is caused.The microstructures of CCD pixels, fiber optic taper and intensifier fiber output panel are analyzed.The process of formation of non-uniformity is illustrated by the composition of real images and the main factors contributing to non-uniformity are described in detail.Severity of non-uniformity is revealed,and its solutions proposed so as to reduce the non-uniformity of ICCD by reducing the fiber diameter of fiber optic taper.